I have verified the VIN as 3B59S both on cab and on frame.
With the brake kits we manufacture I have come across many different combinations that were not in the manual or heritage packets. I have seen AD 3600's with factory dual rear wheels and a standard 8 lug front hub and also with a the extended front hub that were not swaps that's why I asked. Could it have been swapped at some point in its life, maybe but as you asked Why? I've seen single wheel trucks with dually axles so I know they did some odd factory installs, Civil defense trucks and forest service trucks sometimes have these upgrades between 36 and 38's but I have not seen one on a 32 before.
I did find in my data book that there was a 5000 lb GVW package that required suspension special ordered separately. This GVW tag says 5000 lbs. It had 8 leaf single stage springs rear 1550 lbs, 1350 lb. Payload (3/4 Ton) and 17.5 inch wheels which I believe were all 8 lug. So this looks like a legit up fit from the factory just very odd.
