Magnums valves will definitely bang the bore. Been there checked that.

Here's another vote for the 302 casting. Having run them on a 273, I was very pleased with their performance.

Besides, it *might* be tough to find a 0.060" over 273 piston without going custom.

I think this is a cool project and am looking forward to updates. I used to get 19-20 mpg out of my '68 Coronet, BBD 2bbl, points ignition/318/904/2.76 on the highway if I took it easy.