The NAG-1 (LX/LC cars) and 545RFE (Trucks) are all computer controlled. I don't know of any stand alone controllers for these transmissions. If you want overdrive, go 727 with a gear vendor or an early 518 without a computer controlled governor. There is little to no support in the aftermarket for these transmissions outside of a stock computer/harness retrofit application that includes the engine control for fuel injection.