1964 Dart GT convertible back seat

The seat frame is the right width, but it seems like it's too deep.

I had the seat out last night putting some rear seat belts in for the kids. I still couldn't get the seat all the way back far enough to get it to latch on those hooks welded to the floor pan. I even tried a nailbar to try and guide the seat under the brackets that the seat back bolts to, but I didn't want to rip the vinyl by shoving it under those brackets if I don't have to.