73-88 Chevy 14 bolt. They had a dually model that was 63" WMS-WMS. Which is pretty much dead on what yours is. They are a little hard to come by though. The 14 bolt that was in Single wheeled 3/4 ton and 1 tons will also work. They are refered to as the 67" axle.
You can use the hubs off of your Eaton rearend on the 14 bolt, you'll just need to get the correct bearings. I can get that info if you want. With this setup you'll have around a 65 WMS, which is perfectly fine. You'll have to adapt the brakes to work though. GM had quite a few different brake drum setups, so it shouldn't be a really big issue.
The 15" rims like the 3600's used will fit over the 14 bolt hubs and clear the drums only on the models with the drums on the backside of the hub. The 15" wheels won't work the drums that are slip on.
