I had a body shop put rear seatbelt provisions in my 65: Drilled and tapped 4
4" x 6" x 1/2" steel plates for the seatbelt bolts. Drilled roughly 1/2" holes in the floorpan for the bolts to pass through. Welded plates to inside of floorpan. Welding was done around the perimeter of the plate on the inside and around the bolt opening on the outside. The shop was also working on a 67 Chevelle with factory rear belts, so that was used for determining the position. They are roughly even with the lower edge of the back seat, as Cam says.
I remember being satasfied that my arrangement is significantly stronger than the 67 factory setup. I could make some measurements tonight if you would like. I would urge you not to just bolt the seatbelts to the floor pan. It is important to spread the force of impact over a larger area of the floorpan.
According to the 65 GM info packet, the optional rear seatbelts were the same belts as the standard (non-retracting) front belts. I believe only a few hundred of these were actually installed in 65. I found a pair of front belts in a 66 Buick that are the same as my front belts, so I now have a matching set of four belts.
Hope this helps. --- Carl
PS: My two brothers and I more or less grew up in the back seat of this car, without the benefit of seatbelts. But I did not like the idea of making my family and friends ride without belts.
[This message has been edited by Carl Brune (edited 04-28-99).]
