You cant use too big of a cam with the converter an compression. I used a MP purpleshaft 268/272 .455 lift cam in mine with an LD340 intake. It ran really strong and very docile. Had J heads w/ 1.88 intake valves mildly ported. Shortblock was stock. The factory 340 intake is fine but a LD340 or performer RPM airgap would be better. Dont waste your money on a Performer as it is no better than a stock 340 manifold. Nothing wrong with 308 heads. Port match them and clean up the bowls. cheap and easy HP. 750 holley carb or TQ will work nicely on this engine.