from your pics it does look like the shaft it too long for the alloy hubs, u can see the dog bone end is pushed all the way into the diff cup & when u tighten it it binds.

ok your cheepest solution will be to get some stock drive shafts for the rear, ( Just to make shure test ur front shafts in the rear) if that works just copy the front.

Soon im planing to get some alloy hubs for my car, but i plan to mesure the diffrence with a vernier & file down the alloy one.
its either the recess for the shaft or the tabs sticking out. It should be very easy to file it with a fine file & a right angle ssqure