Couple of thoughts --
-- The seat covers might look great, but with their age, the fabric backing might be dry-rotted, which might cause problems in taking them off and then re-stretching them on installation.
-- Seems like YearONE or Legendary used to sell foam seat buns for '65 Fury buckets? I'm thinking they are very close to the '67 and '68 seat buns? Possibly close enough to modify or add-to to get to where you want to go?
-- I think there is a thread in here, from a few years ago, where a member used a hand-held clothes steamer to rejuvenate seat bun foam? As I recall, it might melt any oils which might have accumulated in it, so it returns to its original shape? I was amazed at the pictures.
Take care,
CBODY67