66/67 A and B body Bucket seat frames and slides

Got a question for you or anyone Else here stripped and own a lot of 67 Cudas bought Grandmas 67 notch Deluxe Interior car about 20yrs ago with Bucket seats and Headrests never took it apart Until I got a redone 67 fastbackl Commando Car with redone Buckets seats in it Oldman Mopar and I Tried to put the headrests in the Fastback But there where no provision holes in the rear frames so we could not do it same year cars so could the fastback have 66 back bucket frames or can you only use headrests for 67 on back frames that had headrests ???