My requirements... what to build?

Nice car! Love the Cragars. Keep the 318, 600 cfm 4 barrel on a aluminum intake, Electronic ignition with a performance advance curve from Halifaxhops, 340 exhaust manifolds of you wish with a nice dual exhaust system. I would upgrade the rear end to a 8 3/4 with a 3.55 gear. You could go a step further by changing the cam. Don't go too big or you'll end up putting a higher stall converter in just to make it work which is ok if you want to go another step further. Calling the cam companies is your best bet. Keep it simple