While I would not be interested in acquiring or building a 71-73 Mustang SUV or Wagon, I find the thought intriguing. One nice thing about the 71-73 based specialty vehicle, a 429 or even 460 would fit in its engine compartment. For pre-71 Mustangs, a lot of under hood engine bay modifications would have to be made to fit the 429/460 into it.
There is a gentleman out here in the Rochester, NY, area who has a really nice looking "Nomaro," which is a modified 2010 Camaro. Here is a link for anyone interested is what it looks like. The photos do not do it justice. In person and up close it is a work of art.