It could be the H110
there is also this one
http://cgi.ebay.com/ebaymotors/ws/eB...e=STRK:MEWA:IT
..another tow truck but a GMC also with the H110 rear end..he lists it has the 6.17 rear gear ratio. I've only seen the H110 have those.
Note the 5 bolt hubs on the front and the 10 bolts on the rear axle..kinda hard to see on either auctions pics. The rims have ten holes but only use 5 on the front.
Looks liike a definate swap with the disc on the first Chevs auction....could been a swap to one of those disc kits..those rear drums are even harder to find than the 71-72 dually 1 ton ones.