[Richard]

Personally, I am a fan of using off the shelf parts for wear items like brakes. Reason I used the 2006 2500HD rear axle with disk and 2009 Ram 3500 brakes on my custom D60 front axle in my build. Rear axle width is real close to the front axle width (stock) on my 72 K10. Rear axle matches front now instead of being shorter like stock. Your 72 K5 would have the same axles as my K10. There is a six lug axle in the same year that would fit your needs. Details can be seen in my build thread.