I have not seen any rear seat that is a direct bolt in that will fit. One guy on here...I forget his name...split the rear seat in the middle and narrowed it. DSE did the same thing on their '65 wagon build if you search their website...they have a ton of good pics.
I made my own mini tubs. So now i am working on the rear seat . Take the seat and sit it into place mark all the spots that need to be cut to make it fit reweld any rods back into place for the strength and refit . not as hard as it sounds and you get to keep your rear seat looking stock on the inside , just a thought. Good Luck.