Doing more research, my 91 Vehicle Communications Diagnostic book shows that there is continuity between the SBEC and the CCD diagnostic connector, so yes there is still hope that you can do this. However, I don't know why you are still getting errors on your traveler.
Another SBEC will not really help. At the very most you can verify which bus your traveler uses if it is indeed not communicating because of a bus protocol mismatch but there is no telling if it will run your car correctly.
As far as using an oscilloscope, you can potentially use one to discern which bus your vehicle is using. The difference between the two buses is simply one has a faster baud rate than the other.
As far as using twisted pair wiring, as long as you twist your wiring at least once every six inches you'll be good to go. Doesn't really matter what wiring you are using.