Which heads to use on my 383?

Either head will run about the same if the same work is odne. You can mill them down alot. My last BB had the 346 heads milled down so much they were almost closed chambers.

The only problem with that is the quench is bad and you could have detanation problems even with compression in the 9.5:1 range or lower. Mine needed some 110 mixed in when it was hot out or it wouldne be happy.