Unless you know what you are doing, I would caution you from just starting to replace parts. You need to see if he replaced the EEC and./or O2 harness or converted the existing one. Different years and 5sp vs AOD have different EEC and O2 Pinouts. First place to check is on the 60 Pin EEC connector- see if there are any wires spliced in and look at the factory pinout for that year and transmission vs. what you have now. There are several sources including www.veryuseful.com for reference. Gotta say been a long time since someone went backwards to SD from Mass Air.