Rebuilding Original Engine 383-s Fastback

The KBs are a good piston. 10:1 with factory heads will be a handful to tune - I'd alter your requirement for that. Have the block blueprinted, run the steel shim gasket, and use the chamber size to set the compression around 9.5:1. That more than likely will require milling beyond a basic clean up which will mean you probably will need custom pushrods and milling the intake flange on the heads As I said - there are no shelf number pistons that will give more than 10:1 using factory heads on a 383. Custom pistons would but you start having issues with detonation and that huge chamber so the camshaft has to be larger.