I have seen them on Taco's too. not sure of BS, but funny you got that pic form some one in Montana. I might have seen that rig the other day.
sorry not much help. maybe try a tire place and see if they can answer that question.
I was looking at FJ wheels and the dealer couldn't tell me either. they suggested a tire place.
if I have time I will stop by my local tire place and ask.
I think the Taco/4th gen wheels are closer to a 5.5 inch backspace.