When I did the conversion on my 73 4/4 I did not need to replace the prop shaft. I just replaced the yoke which has the correct splines for the T-9. I also had to replace the original mechanical clutch linkage with a hydraulic set up. I got mine from Retro Ford.
If you have someone go over the box, have them put a drain plug in the bottom. Makes it much easier to get all the gearbox fluid out when doing a change.
