If you search darkside rear tire here in the forum, you should find the sizes of car tire that work with the swingarm.
I'll post pics when the actual build starts. Right now we're sweating that damned stator. My kid is working on his masters at PSU, hosting three Last Call Trivia nights at three different bars here in Portland (His mom and I along with four others are a team known as Bad Dad Jokes) so time over here to help with the bike is hard to come by.
That TRX frame is due here today via UPS. The A arms got here last week, and the hubs will be here next week.
As I see it, after the stator, it should go something like this:
Pull the radiator, and associated parts.
Cut the forks, just below the triple tree, and cap them for looks.
Weld the TRX frame to the Vulcan, while matching the steering shaft to the center of the triple tree. I'm thinking it might be easier to put in a universal joint just below the tree.
Need to find a 4 x 144 to 4 x 100 adapter, failing that, some 17 x 7 quad wheels with a 4 x 144 pattern.
Relocate the radiator up front. I have a bad feeling about that...
Make a cowl to cover the TRX frame and radiator fittings.
I've done custom wood working as a hobby for 53 years (started when I was 8) so the front end cowl will likely be something to see...