Are you sure there's no bolt plate or U bolts holding the differential U joint in place? I've never seen a driveshaft that you had to remove the joints to get it off...
Even 2 piece driveshafts with a center support work this way.
My '90 chev has 2 U bolts holding the shaft on at the differential. I can have it off in under 5 min. with one wrench.