use the KB quench dome pistons, I'd suggest the lower compression ones with a short cam
or if you have gears etc the higher compression ones with a bigger cam
here is the standard 340 piston
KB Hyper Piston- Chry 340 Rod 6.123 Flat Top 6cc 2V [KB243KTM] - $448.62 : United Engine & Machine Co. Incorporated, Performance Pistons
but I'd stroke it with a 360 crank and use one of the top three pistons from this list otherwise with stock crank think custom pistons of similar design
Chrysler : United Engine & Machine Co. Incorporated, Performance Pistons
click on the piston picture to get cr info
cc your heads or get a real number not the advertised number which is smaller than reality
IF you go Flat top pistons you have to deal with detonation on the street with street gas
The other option is a 4" crank and similar desigh pistons to the three above
what you are doing is moving all of the combustion chamber under the spark plug, providing quench by putting the piston and head cold surfaces close to each other and providing squish when the gas is forced out of the intake side of the chamber
I (and others sharper than I) helped design these pistons with then KB Chief engineer John Erb specifically for what you are trying to do
you can make it run a lot better than you ever can with flat tops
what gears and where do you want your torque/ power band?
iron heads 9.5 is pushing it without having to screw with (retard) the timing which causes more heat- a vicious circle
stock cam has really long ramps so late intake close hides the higher compression