I'm about to start a KH conversion from a freight hauler to a SUPER DUMP, dump truck.

What have you guys used on previous projects for the drop axle rims, & tires. With the standard Tamiya tires/wheels, I find they are too big to fit. I need to fit 3 lift axles underneath this thing. The frame rails I have, from a Grand Hauler aren't quite long enough to accommodate this many axles. I can ONLY fit 2, & then there isn't enough room for the third, & still have fuel tanks.
If you don't know what a SUPER DUMP is, here's a YouTube video of it. It even features a construction company local to my area.
https://www.youtube.com/watch?v=T-7mm9btEXE
These things are FAST becoming popular here in Washington State, due to the high volume of materials they can legally haul, & still maintain maneuverability in tight spaces.