I'm a fairly big person (a shade under 6 foot, 278 pounds). My upper body is larger than my rump area. Hulk, Dr. Doom and Dueling Dragons have ride seats located at the queue enterance. Try them out. I was able to ride Hulk in a normal coaster seat but the buckle just barely fit (although it took two workers to get the buckle to latch. One to push, the other to buckle). The special seat is located in rows three and six and has two buckles. I had plenty of room in those seats but there is only two seats per train with this configuration (I think one per row should be the norm).
Hope this helps,