340 Piston to valve clearance w/RHS heads

Yes the piston rock goes away when the motor is warmed up. Problem is the warm up. Those do run tight for a forged piston but looser than the hypers.

Most problems with KB hypers is not running a .030 top ring gap. That large gap closes up as it heats up, The top ring is higher up and gets more heat. Most engine builders today know that those hypers need large ring gaps. Hypers been out for over 15 years now i believe. Pushing 20 years.

If they were that bad they would not make them anymore. The lighter pistons make everything easier on the engine. This isn't 1970 anymore, why use 1970 tech. I see your going with a roller cam, I went old fashion and use Valvoline not street legal oil with zinc. But pistons I went the newer way. I don't baby my engine either