[CC69Rat]

JWQ - welcome to the board.

As previously mentioned, there were two different widths of the rear axle housings in our trucks. The early trucks had a more narrow housing width. Around the mid year production in 1970, GM added 3/4" width to each side to adjust the rear track width. When they started offering disk brakes in 71 the front track width was widened .. the extra width in the rear was necessary to kinda match them up.

So the 63- early 70 trucks will have the narrow axle housing from the factory. If you lay down under the truck and measure from the back of your rear brake backing plate over to the other side in the same place. This width will be 55.5" all narrow housings will be 6 lug.

In the middle of 1970, and the introduction of the wider housing.. they were still 6 lug. But, the plate to plate measurement will be 57"

71-72 trucks would be 5 lug of course.. 57" wide

The 70 trucks could be either. 55.5"or 57" housing. 6 lug. I guess they just used up the inventory of the narrow housings until they were gone. So your truck could be either. If you decide to swap axles this is pretty important to find the correct ones

55.5" early housing will use a 30.5" axle if you measure from the end of the axle splines to the wheel mounting surface of the axle. The late axles are 31 5/16" long.

63-70 conversion axles from Moser are really awesome. I have converted several. It's not terribly difficult.

If your housing is 55.5, you want the 63-70 axles. 57 get the later ones


There are a ton more wheel options for 5 lug.. thats really the biggest reason I think people swap them. Check out The Little Shop in Nashville for your brakes, drop kit, 5 or 6 lug conversion spindles. They'll have anything you need

Hope this helps!