Your friend is going to pull heads, so do that 1st and measure piston in hole at TDC. Check condition of bores too.
Then build ur plan.
I'd mill some cheap 516's, add the 1.74 exh valve, bowlport & mill .060 or so.

I have a .020 over 64 383, it had milled 516's, 284/484 equivalent type hydro cam, flattops w/no brows and it sounds racey, made good power......"on a budget".

Compression & port velocity rules on the street with a manual trans.