I don't know if I am going to do it or not right now.
The rpm difference, I can live with if I have to. I just need a car.
I have been looking over the schematics for these transmissions and noticed that the shift pattern on the 4t40 is only half backwards.
The A solenoid is used the same on both. It is the B solenoid that is switched backwards. All I have to do is put a PNP transistor in the solenoid wire and it will do the exact opposite.
I have also thought about using the 4t60 if I can splice the CV shafts. I am going to take the inboard end from the 4t60 shaft and put it on the 4t40 shaft and see if it fits. If it does then I will use the 4t60.