STANFORD — Adding two starting-caliber offensive linemen early in free agency showed how badly the 49ers wanted an upgrade in front of quarterback Jimmy Garoppolo.

Center Weston Richburg and guard Jonathan Cooper likely won’t be the only newcomers to that line. Next month’s draft could also reap a potential starter.

In that case, why did general manager John Lynch spend Thursday at Stanford’s pro day rather than at Notre Dame’s, where the Irish boast top prospects in guard Quenton Nelson and tackle Mike McGlinchey?

“As this draft approaches, you just want good office time,” Lynch responded. “Last year we got out and saw quarterbacks.”

Quick refresher: Lynch canvassed the country before last year’s draft to scout top quarterbacks, including attending Notre Dame’s workout to see quarterback DeShone Kizer. Meanwhile, Stanford held its session that same day with defensive tackle Solomon Thomas, the 49ers’ eventual top pick at No. 3 overall. The 49ers passed on Kizer, selected C.J. Beathard in the third round and ultimately found their franchise quarterback through an Oct. 30 trade with the New England Patriots for Jimmy Garoppolo.

“Film is our best friend right now,” Lynch continued. “We’ve got enough people out and about. We’ll have private workouts that I may get out and see. This one was too easy.”

This one Thursday was in the 49ers’ backyard at Lynch’s alma mater, Stanford, where he said he wouldn’t rule out drafting an offensive lineman (from anywhere) if it meant improving the roster.

A week after signing Richburg and trading away Daniel Kilgore to change starting centers, the 49ers signed journeyman Jonathan Cooper on Tuesday to compete for either guard spot.

Cooper, Lynch said, will conservatively be brought along after surgery earlier this year to repair a medial collateral ligament he tore in the Dallas Cowboys season finale.

“He played very well in our minds for Dallas last year and kind of resurrected his career,” Lynch said. “He’s battled injuries but we really like the way he plays. We think he’s a very good fit for what we do.”

Cooper started 13 games at left guard last season with the Cowboys, after starting his career as a No. 7 overall draft pick of the Arizona Cardinals in 2013 before bouncing to the New England Patriots, Cleveland Browns and then the Cowboys.

So which side will Cooper play?

“We’re going to work all that out,” Lynch said.

Cooper’s competition for now is Laken Tomlinson, last year’s starter at left guard, and Joshua Garnett, a 2016 first-round pick from Stanford who did not play last season while recovering from knee surgery and re-conditioning his body.

On Tomlinson, Lynch said: “Laken played very well, the longer he was there. People forget with Laken he came Week 1 and was kind of forced fed. We didn’t have many options. We saw a guy get better throughout the season so he’ll get his opportunity.”

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On Garnett, Lynch said: “Josh is doing very well. We’ll continue to watch him. But he did a great job with the time he had last year to improve himself as a player. He really remade his body and we’re really proud of the work he’s done. We look forward to him getting after it in the offseason. … I think he’s excited about it. He’s feeling sexy, as he says.”

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49ers’ injury curse strikes their charter flight to East Coast, MRI truck in West Virginia One more name to keep in mind regarding interior linemen is Erik Magnuson, who made last year’s team as an undrafted rookie out of Michigan and played multiple positions.

On Magnuson, Lynch said: “The nice thing with Magnuson he can and did play it all. Shoot he played right tackle, guard and can play center. That becomes very valuable. He was a nice surprise last year.”

— Former Packers and Panthers cornerback LaDarius Gunter visited on Thursday, a day after the 49ers hosted Jaylen Watkins.

— The 49ers’ annual Winter Fest last weekend at Squaw Valley was a big hit, with the help of big names in Jimmy Garoppolo and Joe Staley. Said Lynch: “This was the best one yet in terms of fundraising, and it helps having Jimmy and Joe. Auction items start going for more. There was a good level of excitement and a real successful weekend for the 49ers Foundation.”