Yeah, like this other guys said, frame swapping seems like a mixed bag of stuff. I've never seen the 57 Ranchero chassis and the Crown Vic chassis side by side.

I've seen a few guys put the 1961-63 Ford F100 shortbed unibody pickup body on the later model Crown Vic chassis. The big problem with that swap losing the whole mid-section of the bed to accommodate the hump in the rear frame rails.

The Ranchero has 116" wheelbase and the Crown Vic has 114.4". An inch & a half can make a big difference in how the tires fit in the wheel well openings.

And there's always the issue of how they handle vehicle registration in your area. What happens when the VIN on the chassis doesn't match the body? Definitely check this out first. It would suck to put all that work into and not be able to license it!

Good luck with your project whichever way you go with it.