Since the comp 268 cam is really a torque monster, I would think that your peak torque would be around 2800-3000 rpms. The rule of thumb is to get a TC that will stall around 300-500 rpms before your peak. So a 3000-3500 stall might be too much. Plus with 3.55 gears, you should be at 60mph at about 2500 rpms. You really need to know where your engines peak output is in order to choose correctly.
Think about it like this. You want your TC to stall while your close to your peak torque, but not quite there. If you go too high with your stall, you will have missed your peak and your power band will be decreasing. Plus you will be slipping like crazy which will create lots of heat and premature wear on your tranny/TC. It will not be fun to drive.
FWIW, I will be running a 451 with comp 274 or 275 HL (havent decided yet) with 3.23 gears and I plan on going with TCI breakaway which stalls 2400-2800. Call TCI, BM, PTC, Dynamic, etc. and ask them, they will steer you in the right direction.