Tom Pelissero

USA TODAY Sports

Chip Kelly has engineered a quick turnaround in the NFL before. If you want to believe he can do it again, there's something to be said for the San Francisco 49ers not making a major philosophical shift in roster-building.

"With Chip, he says it all the time: He wants to run the football, and he wants to be able to play big-boy ball on both sides of the line of scrimmage," 49ers general manager Trent Baalke told USA TODAY Sports. "From a personnel standpoint, very comfortable with who we have, the direction we're going and how it fits within the schemes that we want to run."

Still, the 49ers are in transition in many ways. That's without even considering the fluid quarterback situation, stoked by Colin Kaepernick's benching in favor of Blaine Gabbert during last season's 5-11 debacle and Kaepernick's trade request in February.

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When Baalke discusses the roster, he tempers his optimism.

Baalke says this might be the deepest defensive line he has been around, featuring the "Twin Towers" from Oregon, Arik Armstead and DeForest Buckner, but he notes it has a long way to go to be the best.

Baalke says he's excited about the young talent at receiver, but he admits it's a "very unproven" group beyond Torrey Smith.

If the 49ers can stabilize the QB spot, with Gabbert or Kaepernick or perhaps rookie sixth-round pick Jeff Driskel, how long will it take to get back on track?

"You hope sooner rather than later," Baalke said. "I know the coaches are excited about what they're seeing and the ability to work with these guys. But until you get them into game competition within the new system, it's really hard to pinpoint."

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Kelly took over a Philadelphia Eagles team that was 4-12 in its final season under Andy Reid and went 10-6 in his first season, winning the NFC East, and went 10-6 again in 2014.

Things unraveled in Philly last year after Kelly wrested personnel control — something he has pledged he won't do with the 49ers, who showed faith in Baalke's rebuilding plan by giving him the opportunity to see it through. How long that'll take remains to be seen.

Quarterback

Kelly has praised Kaepernick's work in rehab from right thumb, left knee and left shoulder surgeries. Word is Kaepernick is getting along well with the new staff and studying hard. It sets up an interesting competition between a multi-talented 28-year-old who has started a Super Bowl and Gabbert, a 2011 first-round pick who has given his career a spark after washing out with the Jacksonville Jaguars. Driskel is an intriguing fit for Kelly's scheme.

Running back

When healthy, Carlos Hyde is one of the NFL's top power backs. But he missed 11 games in his first two seasons, finishing 2015 on injured reserve with a foot injury. Mike Davis, DuJuan Harris and Shaun Draughn also return.

Wide receiver

Barring the unlikely re-signing of 35-year-old Anquan Boldin, the depth chart appears wide open behind Smith, who had 33 catches last season after signing a five-year, $40 million deal. Quinton Patton, Bruce Ellington, DeAndre Smelter and DeAndrew White are in the mix. So is Eric Rogers, who got a $225,000 guarantee to leave the Canadian Football League. Veteran Jerome Simpson is extremely talented but wildly unreliable. Sixth-round pick Aaron Burbridge (Michigan State) is worth watching; he's not a burner but is a tough receiver who fights for the ball.

Tight end

Vance McDonald emerged as a receiving threat after the 49ers dealt Vernon Davis in November and Garrett Celek got hurt. Celek got a four-year, $10 million deal in February. But this group seems wide open, too.

Offensive line

The 49ers think they got the best run-blocking interior lineman in the draft by trading up for Josh Garnett (Stanford). He figures to start at one guard spot. Alex Boone's departure opens the other for Andrew Tiller or perhaps Zane Beadles, who came over after the Jaguars cut him. Five-time Pro Bowl left tackle Joe Staley is the stalwart. Marcus Martin and Daniel Kilgore are competing at center. Tackle Anthony Davis, who sat out last season, said he intends to file for reinstatement but hasn't done it yet, leaving Trent Brown to compete with ex-Buffalo Bill Erik Pears.

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Defensive line

Three-down interior linemen are hard to find, much less ones who stand 6-7 and weigh around 300 pounds. Armstead and Buckner figure as cornerstones of a rotation up front that includes Glenn Dorsey, Quinton Dial, Tony Jerod-Eddie and nose tackles Mike Purcell and Ian Williams. Williams (ankle surgery) might not be available for the start of camp. Rookie fifth-round pick Ronald Blair (Appalachian State) brings versatility. Kaleb Ramsey is starting to come into his own and has a chance to contribute, too.

Linebacker

Baalke says NaVorro Bowman is healthier and more confident than he was a year ago, when he returned from knee reconstruction and led the league in tackles. He's the key piece inside. The 49ers retained Michael Wilhoite as a restricted free agent and also have Gerald Hodges and Ray-Ray Armstrong, both in-season acquisitions a year ago. After failing to record a sack as a rookie, Eli Harold bulked up from 240 to 270 pounds. That could help him get on the field more outside, where Ahmad Brooks has held down one starting spot for five seasons. He's in decline at 32 but seems re-engaged. Aaron Lynch was the other starter a year ago. Corey Lemonier also has played. And lighter, quicker Tank Carradine is competing for pass-rush repetitions after three years miscast as a four-technique.

Secondary

The 49ers have invested a lot of draft resources here — six picks in the first four rounds since 2013, including cornerbacks Will Redmond of Mississippi State (third) and Rashard Robinson of LSU (fourth) this year. Tramaine Brock and Kenneth Acker are the incumbent starters outside. Dontae Johnson also has played. Coming off an anterior cruciate ligament tear, Redmond is expected to be ready for camp. He could play outside or in the slot, depending in part on how they want to deploy versatile Jimmie Ward. Robinson is talented but figures to be rusty after suspensions took him off the field for parts of 2014 and all of 2015. The 49ers exercised their option on safety Eric Reid, who has started all but one game since he was a first-round pick in 2013. Veteran Antoine Bethea was durable before a torn pectoral muscle landed him on injured reserve last season, opening the door for Jaquiski Tartt.

Special teams

Kicker Phil Dawson, 41, is back for an 18th NFL season (third with the 49ers) after converting 88.9% of his field goal tries in 2015. Punter Bradley Pinion and long snapper Kyle Nelson also return. Ellington was the primary punt and kick returner last season.

Coaching

Kelly, 52, remains highly regarded as an offensive mind and will continue to call the offensive plays. But time will tell how well he can apply lessons from his time with the Eagles. Jim O'Neil takes over as defensive coordinator after two seasons in the same job with the Cleveland Browns. Senior defensive assistant/linebackers Jason Tarver, the former Oakland Raiders coordinator, is a respected assistant. Offensive coordinator Curtis Modkins held that title under Chan Gailey with the Buffalo Bills (2010-12) before three years as the Detroit Lions' running backs coach. The longest-tenured 49ers assistant is running backs coach Tom Rathman. Derius Swinton II has spent the past seven years assisting special teams with four NFL teams and gets his first shot as coordinator.

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Follow Tom Pelissero on Twitter @TomPelissero

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