It sounds like your car may have come with 275hp--327. Why not put a crank or turn the crank in the 327? Have any of these heads had a valve job and had hardened seats put in? They were designed for leaded gas and more octaine. To answer your question the 462s should help you overall but they will hurt you on the bottom end . They have bigger valves, 194/150 compared to172/150.The small valve will give you more torque off idle to maybe 3500rpm . Above that the bigger valve and better head will make right much power. I have a round to it car that I may never get round to Its a 66 Impala 4 dr,275hp 327 I did put 2&1/2 exhaust,turbos and ralley wheels on it . It ran pretty good but is now sitting out back going down hill fast.