Correct, the old school method is just that. I have a Snapon adaptor for PVs. Should hold the rated vac for at least 30 sec. Had one a week ago that the diaphram was going south. Was wet on the chamber side also.
This is the Tail Shaft you are talking about not the 4th gear input. A snap ring plier to spread the ring and then just pop the shaft in and the ring should seat and hold everything together. O Reillys has the tool Cheap.
If It ran good then it should run good after a refresh. At 11.5 with an iron head you will need race fuel to get the most out of it though. What did Dad used to run? Pics would be nice of the old Girl, before and after tear down please.