The rods are more of an issue than the pistons. Stock pistons should handle that pressure.
The issue is ensuring you have no detonation. Detonation at 20psi will blow a hole through a forged piston just as well as anything. detonation is also the major cause of rod failure. Though the stock connecting rods are probably the weakest point of the whole bottom end of the motor.
The big issue with that pressure though is keeping the head sealed. People are doing it, though i think they may have o-ringed the heads and ARP head studs and high quality gasket to get it to hold tight.