Looks great, Paul! Here is my progress so far. Like I said a few posts ago, I "found" two 10mm x 1.50 threaded "lugs" cast into the bottom of the swingarm.
I then drew up the mounting plates. The plates will be bolted to the swingarm with two 45mm long bolts through a spacer and two PTFE-impregnated bronze flange bushings. I'll show that when I get them. Everything except the yellow cardboard mockup is on paper.
The parts in yellow will pivot in the vertical direction. The yellow "spacer" at the back will be where the horizontal "axle" will be. Somewhat like a bicycle head tube. That's on paper, too. But one thing at a time.
Everything will be steel for now. For a few reasons. One, I have some 1" tube and 1/2" tube already in the garage. Two, I can weld steel with my mig welder but have no experience with a Tig so... I'll work with what I have for the time being. I've spent $22 on bushings. I hope to build the trailer for less than $100. Most of the cost will be in a tire and shock.
More pics as I progress.