That's a nice trailer Pitster,
I wish I had a motorcycle bone yard to pick from but I have to deal with what I have on hand. I'm also building a trailer for a little different purpose than most do. Mine has to fit my glider and all my flying gear as well as keep it out of the weather.
Here's my progress so far today.
I had a couple of lifeline stanchions that make good forks. I have 3/8 bolts to hold them during construction but will go with straight pins and ringdings for the completed trailer. Maybe pip pins later if I can find some.
A mountain bike head set. Unfortunately the frame part of this is aluminum but I have a plan to deal with that.
Here's the "hitch" part of this deal.
Yes, that's a binnacle instrument pod mount from a boat... your point? heh heh
Once I get the tire and shock arrangement worked out I'll put a bolt right down through that aluminum part to lock that cross frame in place.
OK, back out to work some more.