I just purchased 3 pt belts for the back seat of my 65 coupe...all instructions say to use existing anchor points for the new belts...problem is the ARE NONE...zilch...any clue where the bolts are SUPPOSED to go???
A 65 may not have holes for rear seat belts. Federal guidelines didn't require them until 1966(IIRC). I would recommend drilling 2 holes to put them in. Get an assembly manual from any vendor and it should give you an idea of where. Good luck.
Which mount point do you want information on, the standard lower ones for the lap belts or the new upper one for the 3-point shoulder harness. I believe that is correct about rear seat belts not being required until 1966. I have heard that many '65's have the holes, but not all. The holes are right at the joint between the upper and lower seat halves. The outside hole is just outboard of the seat, in that void under the side trim. The inner holes are mouned just to the left and right if the driveshaft hump. I'm sure somebody has a picture, but contact me if you need me to take one for you.
As far as the upper mount point, there are several options. I have seen retractors on top of the package tray, under the package tray, and bolted to the trunk side of the wheel well. Just make sure any mount point you choose is fairly solid sheet metal and backed up with a large fender washer. Here are some links I have collected on rear shoulder belts. I have done 3-point belts in the front of mine, and have the parts to do 3-point in the rear. I'm contemplating the same project.