I have a front and rear bench from a 63 Dart 4-door available if the will work for you. Padding and covers are shot but would make a great core for a re-do. PM me if interested.
Not totally certain but I think any Dart or Valiant rear seat from a 64, 65 & 66 would work, either a2or4 door. The only early A that wouldn't would be the Barracuda seat as it folds down.
I'd appreciate having the measurements. I'm trying to determine if a Caddy CTS seat will fit in my 69 Dart. I know someone put one in an early A (Dart).