8.25 from a -72 onto a -66 with 8.75?

Don't forget the 8.25 has a 4.5" bolt circle and the 8.75 has a 4" bolt circle (unless it was modified) for the wheels.

I am not sure but are the wheel bases of the 66 and 72 the same? If they are you should be able to swap drive shafts but if they are not then both will need to be modified.