My 1966 dart race car.

It's a little beyond me, but I always thought to go full roller bearings you had to have the case in order to get the end play perfect. It's not a wide spec like when using thrust wasters...
I also think the reason you stripped the splines is while they are the same count, IIRC they are cut on a different angle 904 vs 999. The same thing can happen using the later and larger Cummins-spec components in a pre-OD 727.