There is a lot of confusion regarding 65-70 Mustang fold down seats, specifically their characteristics and interchangability.  The following information details the 1965 Mustang fold down seats, and I have separate guides for other years.  Additionally, this information was recently published in the June 2006 issue of Mustang Monthly.

65 fold down seats are easily identified by the rectangular shaped seat support on the rear panel, and has a corresponding short round stop bumper that rests against it. 65 fold down seats also have only one latch, and as such have only one cutout for the latch in the seat on the passenger side. The latch guide is plastic and mounts with one screw.

This picture shows the rectangular shaped seat support on the rear panel.

This picture shows the round stop bumper unique to 1965 models.

This picture shows the black plastic latch guide.  The latch in 65 is only on the passenger side of the seat.

1965 fastback fold down seat: