I’m in the same boat my Duster is a 71. And I have 72 bucket seat frames n I still have the old foam. I’m wondering if I should use the old. You’re right no one’s making 72 foam because the 72 foam has internal springs molded in the foam. So I either use my 72 buckets as is or get 71 used $1200, or new, $700, frames
This might be an option for you too