Hey mert,
was the car an original bench?
all early years bolt up fine, but the 68 is the only one with locking seat back. if its safety you are after, don't go for anything else, if you can help it.
i had to track one down for my car and ended up getting it off us ebay for us$299. by the time i shipped it, it cost around au$700 delivered.
once i had my seat at home, i was told of one at Mustangs West... google them, they may still have it.
this is my 68 bench seat album
http://s806.photobucket.com/albums/yy342/tim_morrison82/Bench%20Seat/i don't have one for sale, but i can sympathise as they are hard to find!
hope you get lucky.
