I have a 1978 chevy pickup 4x4, 4 speed with a 3.73 posi rearend and a 350 in it that I use for towing cars and stuff, the engine has flat top pistons with standard bore, headers and a 600 cfm edelbrock carb,it has a step above rv cam in it with stock 76cc heads, and true duel exhaust with glasspacks, I was wanting to get more horsepower for it like from 400-450, and so what should I do to the engine to get it there