the DOHC bumper fits on the SOHC car as a bolt on directly; however, the SOHC bumper as it wraps around, the portion that lies below the "side molding" (stripe that is on the middle of the doors and runs down the side of the car) doesnt exist on the DOHC bumper because its part of the fender itself.

so if you want to make it easy, swap DOHC s13 fenders and bumper or get the SOHC front bumper extended or custom filled or you'll have a gaping hole there.