Yes older engines use forged pistons, but if it was me I’d go 10 psi max even with those. As far as injectors you’d need to know what psi you’ll be running and what power level you’re expecting to be at, 36-42 lb/hr is probably what you’ll end up with, and you’ll also need to upgrade your fuel pump.
Stock 302s with forged pistons can be had cheap ($200?) may be best off to buy a used engine and build it on a stand then swap it in.