
First off....Props for Ingenuity and trying to make it work!
Second, We have to remember that any wheel that is attached to an A-Arm....Off set will effect handling.
Think of your fronts on any quad....offset always is important and changing results in Camber changes....toe in....etc.
An IRS rear is gonna be tricky to make wider.
Aftermarket Rear A-Arms will be a long ways away.
Best bet seems to be find a 12" Wheel with about the same Offset and you'll be ok.
It looks good.....but the end performance is all that is really important.