High Back Buckets from a 74 Charger

We are building a '71 Demon, original bench seat car. A guy brought us over some high back bucket seats and buddy seat from what he says is a '74 Charger.

I've been looking at numerous posts and it seems there was some kind of conversion from a "spring" back to no back. I pulled off the plastic seat back and I did not see any springs, just a hollow area with foam on the front side.

Aside from the seat tracks, is it possible to buy the correct '71 Demon seat foam and covers for these seats and have them work?

Thanks for your help, Bill