Best donor for MPI

I would use the stuff you have, it sounds like you have the obd 2 harness that would work fine with the 5.9, and you should be able to use whatever year obd2 PCM with it you want. I don't have any experience tuning those though, so I can't help you there. Depending on the year engine you may have to use sensors off the 5.2, because of the connector differences. I have a 95 Dakota that was a v6 and now has a 99 ish 5.9 in it, and I took the sensors from the six, so I wouldn't worry too much about mix/match.