k so which engine

Ok you will probably need to shave the heads some to clean them up but to take a whack off for compression is something I wouldn't do. You will have to sit down and do the math to figure out how much compression you want. Since you said you want flat tops you will have to find pistons that are close to zero deck so you don't have to take much off the deck to achieve zero deck or slightly positive deck. Heads I figure you'll use what you got which probably is X heads. They are great heads and with mild porting will flow very good for 340 cubic inches. They do not have harden valve seats so you need to either replace them or run lead substitute in you gas. I ran it for years and never had a problem and the seats looked great after all those miles. The purple series MP cams are very popular and make good hp but there are more modern designs like comp extreme that will make more power. Intake...air gaps are hard to beat so I would go with that in a heart beat. Carb is up to what you can afford. Vacuum secondaries are cheap but get a double pumper in the 650-750cfm range if you can. Also don't for get headers and some nice 2.5 inch exhaust.