I want to replace the entire front & rear axel housings with the axels inside, the drums, etc. These are completely rebuilt & would be replacing trashed stuff that would cost more to rebuild than to replace with this.
so, yer putting 68 parts into a newer 73?  ouble-triple check, but 68 was a transition year for the ball-claw axles and the "slightly" better coarse spline birfield axles. The 68 might de a downgrade. Also make sure the side gears in the diff are fine spline, coarse spline is again another downgrade.
My mid 68 had the birfs, and other wise is very similar to the later drum brake axles. I have a 75 in my garage now and the brake lines are different than the 68 was. The routing on the 68 had the rubber hoses coming off the frame on each side, the 75 has a single down the center (more driver side) and tee. If ya swap the brake lines, or use the 73 stuff all will be good. Those are the only differences I am aware of, but like Woody said if they are earlier axles they may have the ball and claw style joints. Ask the person that rebuilt them.