you don't need to spend the money on head work etc on the stroker. you also only need to upgrade valve train and or springs if you were building something crazy. if your set on stroking no need to buy a kit. just get a 4.2 crank and rods from a free to cheap 4.2 a set of oversized pistons of whatever bore you want from a stock rebuild kit. a stock 7120 4.0 head and go. if you upgrade the cam to a hesco rv06b you will need some minor head work to seat the new valve springs as the head needs to be machined slighly.
stock stamped rockers are fine way past 300 hp. i just built a 4.7 that is going into my jeep as soon as i measure for push rods.