That is an interesting trailer! Looks like it has some type of torsional axle system. That's what a lot of travel trailers come with now made by Dexter axle. Sort of amazed that it was around back then.
I was curious on what might be out there. From what I've read online it looks like it might have been sold by Sears. They had the Elgin motors and you could also buy Elgin wood boats and trailers. The boat thing surprised me. Now, trying to figure out who made trailers for Sears may be a little more difficult. Even found a link for Sears Parts Direct to get boat trailer parts. Who knows, maybe you can get some kind of info out of them. Wouldn't that be a hoot. Anyway, here are some links I found and maybe you've already seen them. The person at the Elgin Outboard site may be able to help you out.
Good luck with your project.
Kirkhttps://forums.iboats.com/forum/general ... rs-trailerhttps://www.searspartsdirect.com/model- ... 05400.htmlhttp://www.elginoutboard.com/sears-cata ... es/1953-2/http://www.woodyboater.com/blog/2013/03 ... y-made-it/