[cletrac (RIP)]

Here's the measurements off the 2B1. These measurements should be the same as you need since everything is in the same place.
-width to outside of box sides 83 1/2"
-length to outside of box ends 79 1/2"
-floor surface to top of box 22"
-height of wheel wells 12 1/2"
-front of box to front of wheel well 21 1/2"
-rear of box to rear of wheel well 21 1/2"
-length of wheel well 36 1/2"
-top of box to top of wheel well 12 1/2
-width between insides of wheel wells 45"
-distance between sills above frame 28 1/2"
-distance between outside of sills 36"
The side boards will be 6 1/2" by 1" so you'll have to start with 2x8s and plane them down to size. The floor planks are 1 1/2" thick so 2x6s will work. It'll likely use those 1/4" x 1" strips like my 2A1 uses. The panels will use those 1/8" x 1" flat irons for edging too.
This pic shows some of the construction techniques. You can see how they made the angle iron uprights.