307
Uh, guy, I think I would take a chill pill till after the first of the year. You may need the 307 block as an anchor to keep us from falling of the fisical cliff. LOL.
Seriously, if the idea is to save money and use what you have, why spend alot of money on a special set of pistons. For the difference in price of special pistons you could buy a 4 bolt 350 block and a set of $400 forged pistons with a dome. If you want RPM, put in a 327 or 383 crank with bearing spacers. It will put that Willys another foot higher with that round tube chrome rear bumper filled with lead.