He'd have to put on probably a good 10 lbs., IMO. He's listed at 6'3" 300 lbs. Hood finished with 31 Tackles and 1.5 Sacks in 2011. The main thing with Hood is that he needs to be able to take on the blocks and not get swallowed up and pushed around at the point of attack. That's absolutely paramount at NT.
I know back when he was drafted and up through last year as well we talked about the possibility of moving him to NT. Steve McLendon is only listed at 280 lbs. but he is very strong at the point of attack, he just needs to get experience. I'm not sure about putting Hood at NT full time. He doesn't always make the play but there were many times when he was helping to corral the running back into the arms of another Steeler, or forcing the Quarterback to slide right into the grasp of a teammate.
Personally I'd like to see McLendon put on some weight as well, he's listed at 6'4" 280 lbs for this season. Just to compare, Chris Hoke is 6'2" 305 lbs. Casey is obviously the biggest player and move immovable of the 4 we're talking about. His status is up in the air right now because of his salary; a restructure is in order for him to return.
In any event, since Hoke is most likely done with football and the status of Big Snack still not confirmed, NT is going to be a key position for the Steelers.