Hi modeler#1!
I do not know what is in the kit.
Do you get the rails?
They are pretty difficult to scratch.
And dimensional they would not be the same between a III and IV.
But if you do you could cut the skirts from Evergreen sheet.
Or even a tee style tin can, a kitchen scissor will do.
I am fairly shore I have a reference and can copy you with the dimensions when I am back home.
Thats Friday.
Best Regards
Johan