I put the GV in my 67 Barracuda with the 904. 3:71 gears. The only change I made was lowering the transmission crossmember about an inch and building a new driveline. The electrical work is more serious than the mechanical work.
Well there you go. There was really not much needed for it to fit the tunnel at least in my case. The electrical is not bad, especially if you use it as just an overdrive. I know swapping to a 5-speed (Tremec) from a 4-speed was lots more work.
