There's only one "type" of 48. There are "rumors" of one with Ram Air IV chambers, but is still ellusive. We've seen them with chamber volume anywhere from 68 to 74 CCs.
Though Pontiac installed the large-valve heads on 350, we try to discourage the practice. We've found the small-valve heads can actually make more "usable" power with 350. The 2.11" intake valve is restricted ("shrouded") quite badly by the cylinder wall. Using the 1.96" valve allows more air/fuel mixture into the cylinder.
I would suggest 17s or 47s for this. A little port work, screw-in studs, and you're 350 will LIKE it! A Comp XE262H will make it "silly" with good carb (750 or smaller), intake ("Performer" is adequate for 350) and smaller (1 5/8") headers.
Should make at LEAST 350 HP, and over 400 lb. ft. of torque. It really messes with a Chevy boy when you beat HIS 350 with yours...!!! Contrary to popular belief, it CAN be done!
