For the most part, the Mets have downplayed immediate expectations for Matt Harvey. They’d like him to stay healthy and continue developing into a potential top of the rotation starter. One of the few men in the organization who has been an ace is careful to toe the party line, but can’t help make the comparison that has come to his mind since he met the right-hander two years ago. “Just the way he handles himself on the field, he’s like a young Roger Clemens,” Frank Viola said of the 23-year-old who made 10 starts for the Mets after being called up in 2012. “And I don’t mean stuff-wise, necessarily. But when he’s on the mound, you know he’s a professional. That’s how Roger was.” Viola is heading into his second season as the pitching coach for the Mets’ Class-A affiliate in Savannah, Ga., and has spent nearly all his time during spring training on the back fields, working with the organization’s younger minor leaguers. Still, it’s Harvey who has made the biggest impression. “On the field, you knew Roger was the man and he showed you why he was the man,” said Viola, who won 20 games for the Mets in 1990 and was Clemens’ teammate in Boston from 1992-94. “Matt’s the same way. Off the field, that’s a different story. I don’t know Matt’s personality very well, but when I got here, he stood out immediately and he’s set the precedent for what’s going on here.”