Well, with the LT4 cam ( if that is the one you have), Vortec heads and the right intake (Performer RPM) and headers, it should make far more than 275hp. I would estimate around 350hp at the crank provided it has at least 9:1 compression when you are done. Use steel shim head gaskets as they will bump the compression a bit.
1985 Cutlass Supreme Brougham (ex pizza delivery beater with 240,000 miles):
355 Chevy- 9.5:1 compression, Comp XE 262 cam, World S/R Torquer heads with 2.02's, Edelbrock Performer, 800CFM Q jet, Camaro ram air system,Edelbrock headers, Comp Magnum roller tip rockers,TH 200 4R, 3.23 rear, aluminum hood, IROC steering box, poly bushings, Eibach springs, etc. Cutlass build thread here: viewtopic.php?t=4982
Also: The Thing That Won't Die-1998 Nissan Frontier, 340,000 miles of pizza delivery.