Andrew, one other thought, I don't know about REO, but as you probably know, the rear axle assemblies for many trucks were made by just a few companies, such as Dana, Spicer, etc. If there is any ID at all on the rear axle, that may help. I know, you may have already checked that possibility, but it's just a thought. I also did a Google search on REO trucks, found that in 1957 REO became a subsidiary of White Motor Co. White merged REO with Diamond T which became Diamond-REO. Later, White Motor Co. was taken over by Volvo who currently owns the REO brand name. Sometimes by following a "trail" like this you can find that the current owner of a brand can supply parts. As I said, just some thoughts. You might like to check REO out on Google, it's interesting. Sorry I can't be of more help, If I find anything further I will let you know. Lowell.