I could rattle on for hours about D8 Final Drives from the first Series H through to the end of the flat drive D8K's, this year I have only rebuilt 4 final drives on D8's, my record is 5 in 2 weeks but they are now in low numbers here in the U.K. still working, although I have 2 full hit engine rebuilds (D342) on the go at the moment, the big changes within the drives are - the outer bearing size in the preload cap, it was smaller than the other 2 taper bearings being changed to all 3 outer bearings being the same, the Dead shaft was changed for a bigger better item with a larger inboard bearing and housing, the duo'cone seating changed from an alloy mounting to a machined area in steel, the tin seal guards changed to again a machined steel type, the intermediate 1 piece gear changed to a 2 section gear held in place by a wire snap ring, there are lots of other small changes but without Serial numbers it's hard / impossible to give you any true facts on your question other than I have fitted D8K F/Drives into a D8H, the outer hub C type collars on a K have 4 bolt mounting, on a D8H they have only 2 bolts, when setting these collars down you have the shims in your left hand and the hub key goes to your right hand on both sides, the outer cap has large lumps 180 deg' on the outer face they line up with the split joint between the frame and the C collar with the chamfer facing forward, I would have rebuilt over the years many of the drives and have photos of 78 of them, on your turning fault you would have to check firstly the brake adjustment then if needed a pressure test that is simple to do but is this D/D or P/Shift.