On my rear axle hubs (Dana 60 full floating axle, just like your), the seal part number is: Timken 455860 The old seal should also have the part number on it as well.
Here is one location for the seals:
https://www.rockauto.com/en/moreinfo...pt=1860&jsn=21
Part number for the bearing cups and cones should also be on the part.
When you take the hubs apart to clean/inspect the bearings. Be sure to coat them with rear axle oil before installing them back into the hub. Once the truck is back on the ground and the rear axle is serviced. Use a jack to pick up one of the rear wheel (as high as you can jack it) to allow the rear end oil to flow to the hub bearings. Let it stay that way for about ten minutes. Then let it down and do the other side. When you place the truck back on the ground, service the rear axle oil level (it should be a little low). I would also drive it for about a thousand miles (don't have to be all at once, just enough to warm up the oil) and recheck the oil level again, oil flow better when it is warmed up.
Also if you wanted to convert to power disc brake, here is what I did:
https://6066gmcclub.com/album.php?albumid=323
If you want info for the power disc brake let me know.