http://www.portcityracecars.com/Chassis-sp-6.html#first-divider
Take a look at the pictures of the offset template body chassis, as well as the road race car (Trans Am series) which is just an un offset template car.
Dirt late models use the same uppers, but some mount them like or similar to this Lazer car
It clamps on those 2 upright bars and is adjustable top to bottom
View attachment 78494
If you look at this picture of my car you can see a sort of hybrid, I have the hoop/ bay bar that port city uses but my uppers clamp to 2 uprights
