I had a 66 Mustang top loader in my 52 Customline in the late 70's. I don't recall modifying the front bearing retainer. Seems like it was a bolt in. Open drive made it easy. Even found a drive shaft at the wrecking yard that fit. No idea what it was from, it was on a rack with hundreds of others. Takes a longer speedometer cable because the drive gear is on the right side to get it out of the way of the shifter. Speedometer cable also has a different transmission end. I think mine was for a 4 x 4.