I recently read an article somewhere online, that gave detailed instructions on hw to bypass c4 computer controls controlling all functions (except the shifter button), of dougnash 4&3 team my. It told which pin connectors to remove/jumper out, to bypass computer controls and make the transmission shift into overdrive by shifter button control only. If anyone knows where I can get a copy of this discussion please let me know as I fm in need of it. It's out there somewhere, can anyone help-daveo

This would be nice to do on my 87 C4. I will keep watching to see if you come up with a solution. 

http://tech.corvettecentral.com/2007/01/servicing-the-overdrive-on-the-43-transmission/

Just did it. Worked like a champ as far as bypassing the o/d.