I think you will need to shorten it. That 2" travel is already needed for when the rear bottoms out.
The front ball & trunnion U-joint of your 64 driveshaft doesn't matter. The rear is a regular cross type, but may not directly fit into the 8-1/4 saddles if it is a smaller diameter. You can check PN's on rockauto and U-joint catalogs (Spicer) to determine ahead of time. In those catalogs, you can find adapter U-joints that have different diameter bearing cups on input and outputs, so could probably deal with above.
You will need to have your 64 driveshaft modified at a driveline shop and they probably have any U-joint adapter needed. If your ball & trunnion is bad, you can still find replacements (I found several cheap recently on ebay). At least lube and reboot it (can use VW split boot). Rather than search for one, a driveline shop might easier replace it with an in-line sliding yoke, as they often do on old Jeeps with those, though would cost much more.
