If your going to repack the bearings you will be pulling the hub anyway so you can get the shoe size then.At one time there was probally some labels on your axles,or if there are some #s on your hubs,a trailer supply shop can tell you what brake shoes you need.
There are all kinds of videos on how to pack bearings on youtube or go to Etrailer.com and they have videos.
2010 298 RLS Eagle
99 Ford F-250
1 Toy Fox Teror
1 Tiny Chi Chi Wa that rules all of the above.