37 Terraplane car vs truck frames

Kdancy

OK, from the manual I see both 117" and 128" commercial frames.
I see 117", 122" for cars
In the 37 brochure I see the Terraplane PU is offered in 117 and 124" wb.
It says the difference in wb is from the back of the cab to center of rear axle. Is just the axle moved back or is the frame extended? Looks to me like just the axle is moved back.
What is the difference in the 117" car vs truck frame besides the torsion bars on the front axles to frame on cars and not on trucks?