benchseat

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Any early A body (1963-66 Dart, Valiant, Barracuda) bench seat should bolt in.
Be aware that 4 doors and wagons had fixed seat backs, 2 door sedans/hardtops and convertibles had hinged seat backs.
You should try a parts wanted ad on this site- it's free.
If you still have no luck locating an original seat, a later '67 and up seat will physically fit in an early A, but the mounting frames will take a bit of work to get them mounted.
Likewise, you might be able to get an early Dakota bench seat to fit, with appropriate modifications.