the lighter guys will have much better feet, so if you can add weight the right way in college (under a strength program) as opposed to the weight most big linemen gain in high school (not exactly strength), you will do better in the long run. i'm not saying 240 is ideal, but i think it's a good thing, if he has the frame. and at 6'5" or 6'6", you definitely have room to add the weight. not to mention that most linemen will redshirt anyway, so there's a whole year to add weight before he plays.
i would add eric winston to your list. he was a highly rated TE out of HS, and left as one of the best LTs in the college game at the time. injuries haven't helped his career, but his production in college was great.