the OBS(old body style) and Superduty 7.3 motors are basically the same. The major differences are the the fuel delivery, injectors and intake. The OBS(94.5-97.5) use single shot injectors which are louder than the splitshot injectors the superduties. The OBS do not use an intercooler and as mentioned the downpipe is flattened to go around the firewall. just stay away from early 99's this is the transition truck ford made going from the obs-superduty. The turbos were much smaller, injector cups....just google it....just keep away from them for did make 7.3 before 94.5, but there were IDI(indirect injected) vs. DI (direct injected) these were non turbos and were powerless dogs. Made good wood haulers though!