67 rear axle???

[kolo]

doing a 67 with my son, we picked up a 79 for the front crossmember swap for 5 lug and disc brakes. We can swap in the 79 rear 12 bolt but will have to change the mounts as the 79 is leaf spring and the 67 is trailing arm. Now the question, does anyone know if the 5 lug axle shafts will just slip into the 6 lug existing axle housing. Both are GM 12 bolts. This would eliminate the need to fabricate new mounts for the later model housing by just swapping the later axle shafts into the older existing housing.