As mentioned before, I got some 1/8th plastic sheet. I had to glue two pieces together to get a basic 36" length (this minus the sections for the sprockets and idlers).
Once "dry," I laid out the height from bottom of where I wanted the road wheels to lay. I then calculated the distances, marked, and set on the stock as you see here:
I had previously gone to Lowes this morning (closer than HobbyTown) in hopes that they may have something I could use for "axles." What I found, that fit these road wheels to a T were:
8-32 threaded rod
and some copper tube:
The copper tube fit perfect into the outer side of the road wheel (where the cap would go):
And, with a wee bit of a drill bit:
Fit nice to the inside of the road wheel OVER it's axle:
I then took three road wheels and three sets of track and laid them out to get an idea of the track spacing:
From there, I measured the space using a caliper and cut some of the tube to length:
And, here are the road wheels, with "spacers" on the track. There is some play in the track, but that's about perfect:
IMO, the copper tube, though you really won't see it, makes for a (as commented before; a tree trunk...)axle.