Rob Ryan’s 3-4 defense is out at Valley Ranch, about to be replaced by Monte Kiffin’s 4-3 Tampa 2 scheme.

How will the Cowboys’ personnel fit into Kiffin’s puzzle?

Here’s a breakdown, with the help of former Cowboys scouting director Larry Lacewell, whose relationship with Kiffin dates to their days as rival assistant coaches at Oklahoma and Nebraska in the 1970s:

DEFENSIVE LINE

The big question about the defensive line is whether the Cowboys will keep Anthony Spencer as a bookend for DeMarcus Ware. Wesley Hitt/Getty Images

The big question is whether the Cowboys keep Anthony Spencer as a bookend for DeMarcus Ware. That’s a financial issue, with Spencer due $10.6 million if the cap-strapped Cowboys use the franchise tag on him again and primed to get paid big bucks if he hits the market after his career year.

“I don’t know if I would,” Lacewell said of keeping Spencer. “I think I could find another guy that was a pretty good player. In my opinion, I’d rather look for a 4-3 guy. I think a rookie can come in. The mental end of it is so much easier than the 3-4 [for defensive ends/outside linebackers].”

Lacewell has no doubt that Ware will be a dominant defensive end in Kiffin’s scheme despite the fact that the perennial Pro Bowler will miss the offseason while recovering from shoulder surgery. Lacewell has little concern about increased wear and tear on Ware as a down lineman, adding to the fact that Ware won’t have to drop in coverage, which might keep him fresher by limiting the amount he has to run.

“He should be similar but better than [Indianapolis’ Dwight Freeney],” Lacewell said. “He’s much stronger and bigger.”

Lacewell, who Jerry Jones brings to training camp every year to help evaluate the defensive personnel, believes Kiffin’s scheme will greatly benefit Jay Ratliff and Jason Hatcher.

Ratliff would primarily be a 1-technique defensive tackle, shading the center and shooting the gap. Lacewell compares him to La’Roi Glover, who made four Pro Bowls playing that role for the Cowboys when Mike Zimmer ran a Kiffin copycat scheme in Dallas.

“It’s going to prolong his career,” Lacewell said of Ratliff, a 31-year-old whose streak of four straight Pro Bowls ended when injuries limited him to six games this season. “And I think it’s going to add misery to the offenses.”

The 6-foot-6, 305-pound Hatcher would be a 3-technique defensive tackle, playing over the outside eye of a guard. Hatcher, who has 8.5 sacks over the past two seasons as a starting defensive end, would get a lot of one-on-one matchups with guards.

“Hatcher would be an outstanding 3 because he can run,” Lacewell said. “He can really fly. He’s going to be able to use his athleticism.”

Sean Lissemore could contribute at both defensive tackle spots. Tyrone Crawford, a third-round pick out of Boise State last season, has potential to play the 3-technique tackle and would be a candidate to start at defensive end if Spencer leaves.

“Monte’s going to love Lissemore and Crawford because they’re try-hard guys who can run,” Lacewell said. “Kiffin is all about speed. They don’t have to be huge guys, but they have to be able to play hard and run.”

LINEBACKERS

Former Cowboys scouting director Larry Lacewell sees a bright future for linebacker Sean Lee in a 4-3 defense. Tim Heitman/US Presswire

Plug Sean Lee in at Mike and Bruce Carter in at Will and pray that the Cowboys’ blossoming stars can stay healthy.

Lacewell on Lee: “He will be absolutely great. He’s already great, but when you become a Mike [in a 4-3], that means you’re a whole-field player. In the 3-4, you’re a half-the-field player a lot of times. It’s just going to add to his greatness.”

Lacewell on Carter, whose speed probably reminds Kiffin of Bucs legend Derrick Brooks: “Oh my gosh, I think he could be a great Willy. Speed guy, can come off the edge and rush the passer, drop back in coverage, really do it all.”

Dan Connor, Alex Albright and Kyle Wilber are among the in-house candidates to be the Sam linebacker. Lacewell is intrigued by the intelligence and toughness of Albright.

SECONDARY

Lacewell laughs at the suggestion that the major investments the Cowboys made in press-man corners last offseason make Kiffin’s scheme a strange fit.

“I get tickled to hear people say, ‘We’re wasting these great corners!’” he said. “Well, where were they?”

That’s a not-so-subtle reminder that the Cowboys ranked 19th in passing defense last season despite signing Brandon Carr to a five-year, $50.1 million deal and trading their first two picks to move up to sixth overall and select Morris Claiborne.

Lacewell said Kiffin asks his corners to play “much more man than you think” despite being based on his Cover 2 looks. Whether they’re playing man or zone, the corners play press a lot, which Lacewell figures will play to the strength of Carr and Claiborne.

When the corners do bail into zone coverage, their mission is to take away the outs and comebacks. That puts pressure on the safeties to cover the post.

That could be a problem.

“The one position I don’t have clear in my head for them is the g--damn safety,” Lacewell said. “I don’t know who it is. I don’t know who the hell it is.”

Asked about Barry Church as a strong safety, Lacewell brightened up a bit: “He’s kind of a Kiffin guy.”

Nobody is saying Church is the next John Lynch, but he is tough and smart, two of the ex-Bucs great’s best attributes. However, Church is also recovering from a torn Achilles tendon, so the Cowboys would be taking a big risk by counting on him.

Asked about Gerald Sensabaugh, Lacewell was lukewarm.

“I’d say they’re more in hunt of two safeties than any other position,” Lacewell said.

If the Cowboys' front office agrees with Lacewell, Texas' Kenny Vaccaro could be a fit in the first round.