I think its a great idea.....go for it

The backend of my '67 is the entire rear chassis of an '88 coupe. It is actually amazing that the dimensons of the Fox chassis are so close to the original car. I need to swap to Ranger axles to get 5 bolt wheels for the back again.
Anything is possible with a welder and careful measurement! My late father told me, "When you can glue metal together you can build anything"

I just rebuilt the stock front end ( with a Shelby drop) as the Fox and later cars differ quite a bit from the older cars dimensionally and with the subframe. I did however add R&P steering using a Taurus rack and Mustang II tie rods coupled to Granada/Monarch brakes

BTW Pete I see you have a '67 Merc. very cool, I have a '64 Park Lane