Sorry about the scale confusion, i'm not very good at this and should probably stop 'helping'. I think you've got what i was trying to say.
Depending on what axles you go with determines what you have to do to adjust their width to what your model needs. Usually you can do a fair amount of width by just changing thicker or thinner 'wheel hexes' adding spacers or going to rims with different 'backspacing'.
http://www.4wheelparts.com/tire-whee...ckspacing.aspx. some people even narrow axles and jb weld new bearing seats, custom milled aluminum axles...
You mentiond new to this so I just wanted you to consider how to use off the shelf parts to get the build cheaper and easier, instead of having a perfect scale truck that now needs custom machined axles and rims and you have to make a mold to cast your own tires. If you have the tools, know a machinist, can get someone on here to make them, or have the money to have a shop do it, perfect! If not we can make the truck scaled to itself and pretty close to the tanks.
Say you wanted to use the 1/18 micro t-rex axle at 3.2" bearing to bearing with stubs to 3.9" as a front axle It would work better on a 1/18 since the 67.75 ÷ 18 = 3.763
remember 1/16 gave us 4.234"
Bump it to 1/14 scale 67.75 ÷ 14 = 4.839 you'd almost be able to run losi mini crawler or exceed maxstone axles.
Unfortunately i'm only seeing the model kit in 1/72, 1/48, 1/35.