you dont need forged pistons for a small shot of NITRUS, its not called NOS, nos is the name of a brand of NITRUS, something asmall like a 50 shot would be okay on a stock 1zz, but i would never do it beucase its gay.
its a pain in the ass refilling the bottle all the time, expecially if your an avid sprayer. it damages your engine way more than a turbo/supercharger ever will, as well as it will tear up your clutch, giving it that so sudden boost of power will tear up a stock clutch...as well as why dont you build a turbo kit, wouldnt cost taht muych more and you dont have to worry aobut keeping a spare motor
and tell whoever told you that you need "new heads" to learn something about cars before they speak