Randy Moss doing all right things in early days as a San Francisco 49er

Seven years later he's come back with an invisibility cloak.

Somewhere behind the cranes and the hard hats and piles of dirt, Moss is working out with the 49ers, but since reporters are usually kept away from practice and Moss has had no interaction with the media since a late night conference call in March, his presence is mostly an article of faith. The 49ers practice field is surrounded by a massive construction project -- the beginnings of their new stadium. On the field, Moss is his own construction project.

Moss, now 35, hasn't played since 2010, when he bounced among three teams, equally nonproductive for all. The 49ers -- whose lack of standout wide receivers may have been the difference between a good season and a trip to the Super Bowl -- signed Moss to a non-risky one-year deal and have been raving about him ever since.

San Francisco coach Jim Harbaugh has made him sound like a cross between Hermione Granger and Vince Lombardi.

"In the classroom he sits in the front row, he soaks up the knowledge and always gives the feedback, too," Harbaugh said recently. "His attendance has been impeccable ... he's like a coach."

Safety Donte Whitner, who played against Moss in '07, when the receiver was having one of the alltime great seasons in history as a member of the Patriots, said, "He's running the same as he's always run. His body looks like a younger Randy Moss."

Moss reportedly has taken 49ers wide receiver Michael Crabtree under his wing. Another who is expected to be pushed by Moss, Kyle Williams, was enthusiastic about the veteran on Tuesday, when the 49ers gathered for an OTA.

"He's had a huge impact," Williams said. "He's a savvy vet. If you can't learn something from somebody like that, you're not paying attention.

"Just the way he goes about his business, the way he works, the way he takes care of himself everyday is something you can learn from. He's one of those guys who leads by example. He's the same guy every single day and that's the best lesson he can give to any of us."

We interrupt this lovefest to point out that it is May, the greatest month in the NFL season. Everyone is fabulous, everyone is fast. Peyton Manning's neck is fine, Rolando McClain can come from a criminal sentencing straight to the practice field and Randy Moss is a stellar citizen.

Much of what is emanating from the 49ers seems to be the product of a vacuum, as though the practice field is sealed off from the spottiness of Moss' career. But just 40 miles up the road, four years ago, Moss was a brutal disappointment. After arriving to much fanfare -- literally a police escort, thanks to Al Davis' theatrical instincts -- Moss appeared to quit on the Raiders and was far from the locker room leader the 49ers are envisioning. He was last seen in Oakland having a screaming tantrum in the locker room because a columnist didn't give him proper respect.

That was a long time ago, on a very bad and dysfunctional team. Since then Moss helped lead the Patriots to an undefeated regular season before suffering a rapid decline. Moss thrived in the Patriots' strict-accountability environment, at least when he was getting the ball. But in early '10 -- amid reports that he was arguing with coaches during games -- he was abruptly unloaded to the Minnesota Vikings. He ended the season in Tennessee, where he had just six catches, and announced his retirement in '11.

But now he's making a comeback. When he signed with the 49ers, Moss said he was attracted by the team's upside and by Harbaugh's enthusiasm.

"I'm very passionate about what I do," Moss said in March. "Football is what I love. I'm ready to get back to the game of football. I think I can still play at a high level."

Under Harbaugh, the 49ers have undergone a massive remodeling, borrowing elements from other architects, like accountability and discipline. They may have built the kind of environment in which Moss can thrive.

But whether he is anything close to the Moss of old will be determined on a stadium field in September. Not behind some cranes on a practice field in May.