There is no differential between the front and rear axles of a typical 4x4 pickup. If the tires are different sizes front-to-rear they will turn at different rates on a hard dry surface. You won't go very far before the whole driveline will bind up, and if you try to force it, something WILL break.
Even if you have four identical tires, a 4x4 will eventually bind up on dry pavement, but sane people don't use 4x4 on dry pavement under normal circumstances.
In the mud or snow, or on wet grass, where the tires can slip, it's a non-issue.
So, as long as you NEVER engage 4x4 on a hard dry surface, a slight difference in tire diameter is not a problem.
It will, however, look a bit too "Beverly Hillbillies" if you ask me. May as well strap Grandma's rocking chair to the roof of the camper and have her come along for the trip!