I suggest you go to the Silvolite website and look over the KB piston selection there. IIRC there are 5 different Keith Black pistons. As you have an open chamber I think it would help to have one with a "quench dome". If at some later time you decide to go closed chamber the quench dome can be machined off.

Actually as you have an open chamber I would suggest Magnum heads and a reverse dome piston set close to the top of the bore..

R.