motor swap 95 galant

I am looking at buying a 95 galant s. the body and interior are in superb shape, but the woman who owns it said that it started idiling funny and then died. i have not personally gotten to check everything out to see why it died. my question is what other differences are there between the sohc motor and the dohc motor. it currently has the sohc but I would like to put the dohc in. will I have to change wiring harness or computer? do they run the same tranny?