Heads

You may want to measure the chamber volume in your 051 heads, too. I've got a set of similar 475A castings from a 1975 truck 360 (also used on later 318 4 barrel) that have a clean up cut on them (.010) that measure 66 ccs with the stock tulip valves in them, or very close to 318 chamber size. So putting nail head valves is going to give you a decrease in chamber volume and an increase in port volume, which is always good in stock iron heads! The small stem 1.94/1.60 chevy valves with good valve job (and maybe hardened exhaust seats in case the stock seats are sunk) that MOPAROFFICIAL official mention are a proven performer. My machine shop guy uses 5/16 stem, but I think the performance advantage for him is more budgetary (I imagine he buys them in bulk). While your into it, you'll want to decide what cam you're going to run with what rockers. Valve lift is pertinent to how the heads are set up.