If you do some engine updates and the computer is bumped up for performance, as well as bigger injectors. you could get to 325 or 350 HP easily. However, the stock engine, with a standard TPI you will get the 265 HP range. Example, this vortec motor from PACE Perf. with a multiport injection and a vortec motor.
http://paceperformance.com/index.asp...D&ProdID=85273