Easy answer, one that even I can explain. You see, there is this scale in model railroading called “G”. Water ever The G stands for, I’ll bet it’s not for consistency.
Doc’s kit is 16 scale feet long in 1:20.3 scale. You model in 1:24 scale, having the same 16 scale feet. BUT, and there is always a but, you are using the same trucks, same track, two scales.
A 4 1/2 ft truck in 1:20.3 comes out to about 6’5" in 1:24. You scaled down the length of the car, but not the length of the trucks.
The same truck rated at 50 tons in 1:20 would be like a 65 toner in 1:24. Your car can haul more payload then Doc’s. I doubt that the Baaar will be more then 50 tons, well maybe with all that rail and steel added.