Not sure why you would want to mess with an adapter.....

I have repined numerous TBI systems to the later PCM. The first time I ever attempted the job it took me a few hours of research to find the wiring diagrams, a couple of hours to match up all the connections, and with the spread sheet I made, took me about 1 hour to swap out the 7747 connectors for the 7426 connectors. I labeled each wire with 7747 pin location with masking tape and a marker and moved them one at a time to the 7427 connectors.

The 4L80E takes 15 wires to run, 12 of which pin into the ECM, 2 go to the VSSB/DRAC and one connection to keyed 12V power. You could add a sub-harness to the existing harness very easily.