Old Car bodies on new car/truck frames........ouch!
I'm not saying it can't be done, I am saying it is very difficult to do it well, and all these years of rodding and rodders say so too.
The addition of a Nova front clip, rear steer(1968-74) or front steer(1975-up), is relatively easy, gives a good upgrade of steering and brakes and ride.
Even easier, if the tread width, will work is the Volare swap BUT it changes the front wheel bolt pattern.
There is really no reason for a complete frame swap unless you have a rare body style with a rotten or broken frame.
Replacing a rearend is so easy and there are so many options out there. The rear springs can be replaced with new on some cars and theold ones rebuilt on all cars.
Yes, if you look at history, you'll find this was tried back in the 50s, 60s, 70s, 80s, 90s, and currently. Many cars were cut up and essentially destroyed during these experiments in "making it easy", just as many cars were cut up and ruined during the Pro-street fad. There seems to be a real deal out there for 49-51 Mercury folks but the rest of us can just step up and do the front clips, front crossmember suspensions and ride, ride, ride.