if you have both cars, and they are both bonnevilles, and both subframes are straight, I would just drop both subframes, and swap them. You'll probably want to swap the rear suspension components too from the 98 so they are matched. Or you could replace just the springs, as the 98 (SSEI) will have stiffer springs. Wiring would come from the 98, along with the PCM. You'll want to replace your fuel pump too for one for the SC motor (I'd buy a new one since they tank is a pain to drop)
Might be a couple other small things, but that'* the basics.
2007 Saturn Aura XR | 1970 Chevy Blazer 4x4 | 1970 GMC 3/4 Suburban 4x4