How to use 6" wheels with AM14U2

[jijiglobe]

So our team wants to use a modified version of the kit chassis with 4 wheels (2 traction on the front, 2 omni on the back). The wheels in question are 6" and to put the axles through the middle mounting holes on the chassis instead of the farthest out ones. We did some measurements for 42 teeth 5mm HTD pulleys and found that the two closest available belt sizes for the hole spacing (about 18.5") were 225T which space 18" apart and 250T which space 20.5" apart.

Is it reasonable to tension out 2" on the top and bottom(potentially using some funky shapes) or should we try something else, like putting a dead pulley in the middle that they both attach to.

We wan't to avoid using chain if possible.