My idea for an engine was much like yours. For my BEC GT40, I built a 1965 SBF 289 (stronger-higher nickel content block) stroked to 302 (i.e. for 5 litre FIA limit) with a flat tappet split-duration cam, roller rockers and webers. Puts out ~400 hp&torque. It has been a good choice for me.
Larry
FYI, it usually takes months to "sort out" any car. So, if you're not a serious mechanic, you'll be way ahead both time-wise and financially if you find one that has gone through the process to include registration with the DMV.
I have one in my BEC GT40 and it has functioned well for three years. My car has a well-built 289 SBF with close to 400 hp. I drive my car sensibly (i.e., I don't rev the engine and dump the clutch, but I do get on it).
Larry