I have a 1997 Saturn scs DOHC an I want to know what all do I got to do to change it over to a SOHC

Thats a big down grade putting in the single cam engine you will lose 24 horse power. To change it over to the single cam I would say you would have to change the underhood fuse box engine harness pcm spark plug wires and you will need a transmission from a single cam engine car. The single cam and dohc engines use different gear ratios in the transmissions. If you leave the dohc transmission in it will set transmission codes and the transmission will never work correctly. Your best bet is to just find a dohc engine. You will need a 1995-1998 dohc engine from a saturn.