I can't help you with the casting numbers, but it otherwise sounds like you've found what you need in one or both of those axles.
Yes, the drums are large and that's a good thing, they'll work well.
Only downside to the drums and being so deep (originaly for dual wheels) is you'll see a lot of the drums from the rear, the single wheels won't cover them.
If you can live with this then only modification that I know of to make it fit your truck is moving the spring pads to match the springs.
If you don't like that look then you can keep the very same backing plate and shoes and purchase new drums intended for a single wheel truck. To make this work you will also need to remove and relocate, or better yet, make/buy new flanges to weld to the axle for the backing plates.
Or there are ready made disc brake brackets and parts list for which rotors and calipers to buy. The downside to this is loss of parking brake in the wheels if you had those. If you do want disc and parking brake they make calipers that do but they're expensive. With disc in the rear you shuld really have them in the front as well. And lastly I'm not sure if the disc are any better than those huge drum brakes?
I know it's been several years now but I have not made progres on this swap myself. Life happens as they say.
However I have not given up and all my parts and pieces are dry and safe waiting for the right oportunity to use them.
Grigg
