I too have been tring to do this mod for my newly aquired 1992 dodge spirt. I have a traveler/message center laying around from the last time I had an AA body (1994 plymouth acclaim) From what I can remember the following holds true:
1) Both cars (a 2.5l/a413) and (3.0l a670) did not have the wiring in the back of the cubby hole.
2) both cars are do not have any of the fancy bells and whistles.
I dont feel that there is any special ECU since my 1989 lebaron had the message center and traveler trip computer with the same engine combo. (a 2.5l a413) . Now I know the computer was replaced in the lebaron before I got it so that rules that out. I do know that chrysler changed the ECU in 1990 to a different configuration. When I look at rock auto they offer two different ECU.. one for federal and one for california emmissions. Other then fuel curves I doubt there is any difference.
I believe the problem here is the bus wiring. I am by no means any specialist in this, but from the fact that it is "serial" and requires "twisted pair" makes me wonder if it is shielded, non shielded kind of like cat 5E network cable. I think the best way to test that is to take a cat5E cable (Twisted pair, shielded) cut both ends off, take two of the wires and hook them up on both ends. The power feeds, illumination, and fuel data should all be working fine if you get the F1-1. I have not tried that since unfortunately, do not have a wafer connection for the traveller