I put a GV unit on a 727 in a Challenger years ago. You shouldn't have to modify the mount unless you need to drop the tail down to get pinion angle correct. I had to beat the living daylights out of the Challenger transmission tunnel so the OD unit would go up high enough to even get the transmission mount to bolt back onto the crossmember. I think you will probably have the same trouble, and it will be the round bell on the end of the GV tail shaft housing and the top corners on the OD unit itself. Measure the driveshaft length to get it right for your car. Did you get the slip yoke for the GV unit? If you did, slide it in until it bottoms out, then pull it back 5/8 of an inch, then measure with the car sitting level. The place that made my driveshaft replaced the end to match the GV slip yoke so I could buy an off the shelf u joint if I ever needed to. I think the slip yoke for the GV is for a GM Turbo 350. If you got all of the wiring with the GV, there should be a box with a lighted toggle switch on it. There should also be a speed sensor that hooks into the speedometer cable with a wire going to that toggle switch box or the dimmer switch button you use to split shift, I can't remember. That should turn the GV off when you drop down to 45 mph. I'll look and see if I have the instructions that came with mine. If I do, I will be glad to send you a copy if it would help. Post a pic of the control box if you can.
