[gringoloco]

ECE and CPP both sell 5-lug axles for the early rears.

You can also make the late axles work in the early housing by using a backing plate spacer or the HD brakes wider drum. This all hinges on how your particular axles are cut, as there may not be a good sealing surface to mate with the outer seals. You should also consider the effect of leverage, as the axles are now sticking out of the housing an additional 3/4". While it may seem minor, you never know what stress it may cause on the axles- remember, the weight of the truck is riding on those outer bearings...

To the OP- I would use the wide '70 housing with the 5-lug axles as a best case scenario- instead of trying to adapt. JMHO