I am currently building a High Performance 300 6 cyl. .... what are the best pistons to achieve power, Ford V8 351, 360, or 390? or dodge like I heard from someone. Thanks for the help.
Stock 300 is a 1.767 CH with a .975 pin. As such the 390 piston (Probe 14833) is the closest to it with a 1.765 CH and the .975 pin but this requires you to be able to go to a 4.080 bore (doubtful on a stock block but I'm no 300-6 expert).
The Probe 12355 piston is a 4.030 bore 1.772 CH but a .912 pin so you would have to have the rods bushed and, assuming a stock piston puts you at zero deck, would put the piston .005 out of the hole (which is fine).
Other than that you're looking at a custom piston or settling for a hyper from KB if you use stock crank and rods.
You could also look for different rods which may require offset grinding of the crank and/or bushing/boring the little end to fit whatever pin size you come up with. You also have to be concerned with big end width when looking at different rods.
There may be other pistons from manufacturers other than what you find on Summit or from Probe so look around for a piston with a.975 pin and something very close to 1.767 CH. You can adjust the block if you find something that is .010 shorter or you can go as much as .010 out of the hole if need be.
So I guess to sum all this up, you have no easy choices for a forged piston but with a bit of inventiveness you can find a combination that will work, its all about the dimensions.
Also keep in mind that the valve reliefs may be all wrong so you may have to flycut whatever you find. All this stuff makes the cost of a custom piston look better and better.