just a few questions about wiring

I have the PCM from the truck that the engine came from. I called Solo Electronics to try to buy a PCM from a truck with a manual transmission. I told the tech that I was putting the 5.9 into a 1965 Dart and using my 904 transmission. He told me that if I wasn't using the instrument cluster from the donor vehicle, that I would never know the difference. If I did use the cluster, I would get a bunch of codes. He says the engine will still run fine. I guess we shall see.
Tom