Gave it more thought, found some 5/8 id x 1.00 od steel sleeves 6 inches long. They are 1018 cars would be good for a experiment but for long term use I wouldwant them heat treated. Now I need a donor trailer and some wheels. This may be a long term project as I collect the items. Will check into bushing manufactures if it works, they can hold the id and od concentric and provide a ground bearing surface.
Ordered the sleeves so at least I will have them laying around if I round up other items.
Cool. Interesting idea. If the fit is right would be no bid deal to some end threads and whatever is appropriate length the, voila, a surprisingly easy retrofit. Hmmmm, now I'm playing with it in my head too.
Tell you what, if you see a cheap donor trailer in my neck of the woods let me know. I'll do the same.

Wonder what Bushtec would sell just an OE axle for? Could use that for mock ups then when satisfied transition to an existing trailer.....