Hiya folks, using the search I just found this thread. I am working on a 94 bbc suburban with a 502, still tbi. The first issue was the 02 voltage toggling between ~450 mv to over 1 volt with just the key on. I grabbed a spare red/blue (6395) assuming they are all the same but maybe not, o2 toggling was gone so at least it is not in the wiring. I haven't driven it yet to see if it will control the 4l80e but I was having some weird issues with the electronic IAC so it dawned on me to research a little.
After reading Dave's post I will hunt down a 7427 and try next week when I am back to work and post what I find.