To answer your question about putting drives in builds....
For me, I did, once, but was not permanently in place, and that was the OLD IMC Chaparall 2E Can-Am car.
Didn't think having a car on a trailer attached to a two vehicle would look right with a driver sitting int the car.....but that's just me.....
Maybe it was just me, but always thought the drivers for the old Grant King sprints/supers looked a little undersized....
Case in point....
I know there are no two vehicles for these 2, because the tow vehicles did not survive the 16-20 different moves in 42 years and the originals to these trailers met their fate before I left for Southern Calif....