I Know this ahs been asked before, but what should I expect out of my stock '85 460 with emission heads and chain set? It has a 600 vac. 2nd holley and factory intake and exhaust manifolds. I will be running dual 2 1/2 with flowmasters and side exit behind the tires. Also what will I gain by putting that older (pre-emissions) chain set in it? how far back do I have to go to get the older set?