This is an odd one. The RCM is highly suspect, but you have addressed that.

So it runs fine, but a lot of instruments/indicators are hysterical. You have a "Serial Buss" error code, that apparently means the ECU can't talk to SOMETHING it wants to talk to. That could be any module on the CAN bus that the ECU is on. Those modules are: Transmission Control Module, Shift Lever Module, SKREEM, Brake Controller, and Instrument Cluster.

LOGICALLY, Id probably suspect the Instrument Cluster because you say the car drives fine. The car can't drive fine if the ECU/SKREEM/Transmission Control/Shift Lever modules have a problem. But the Instrument Cluster in a failed state would not cause the ECU to not be able to run the car.

I do know there have been a FEW IC failures over the years. I'd be sure the battery cables, block to chassis jumper and alternator are good before I tore into that Instrument Cluster. I'd also do James' mod right away:
https://www.crossfireforum.org/forum...le-engine.html

Has this car had flood/water damage in its past?