I had a pair of Super Stock spring mounts in my 70 Charger for years. I used them because they allowed me to drill holes HIGHER on the bracket to lower the car without de-arching the springs. I later had a Gear Vendors overdrive unit in the car. I had a series of vibrations with the GV in the car that always annoyed me. It was a rebuilt first generation unit with a bolted on yoke at the output. I had to use a 4wd style slip and spline driveshaft. I ended up pulling the GV out and went back to a regular 727 setup. At that same time, I put stock spring hangers back in. All the vibrations went away. Trouble is, I can't clearly say where the cause of the vibration was. I'm not sure what the difference in pinion angle is with a 1 3/4" difference in hole position. I do know now that a higher hole position is going the WRONG way for guys building a drag car since the smart move is a static downward pinion angle to counteract the axle rotation at WOT.
