I am going down the same road.
I have a 1972 Duster with later 1973 & Up bucket seats.
I was thinking of having an upholstery shop add a vinyl panel to the 72 seat cover back...so i wouldn't have to worry about/use the hard plastic back panel.
To me it looks like if you use the proper foam it would work.
If you look at a 1972 bucket seats and compare to the later buckets the seat covers seem to have similar lines.
The 1970 & 1971 seats seem to have a much different sewing pattern...so you would need to use that foam with those seat covers.
Seems like the seat frames are close enough in size and shape (if not the same), that even if the factory foam didn't work, that an upholstery shop could custom make the foam if necessary.
There is a shop on Craigslist (local to me), they seem to do a lot of Mopar upholstery work...they might be able to answer the question. Be warned, these guys aren't cheap...
http://detroit.craigslist.org/mcb/pts/3204932128.html
I thought to buy the covers for my Duster first then worry about the foam situation until after I have tried the covers on my existing seats.
But I haven't been able to save up enough money...life keeps getting in the way and my money goes other places.
Paul