I put 3 point static belts into my 57 a couple of years ago. I did this by using information that was on the internet from someone who had done the same thing on his Thunderbird after an accident where he incurred some nasty injuries (sorry I can’t remember his name or which site it was on). My car has a soft top so I also wanted to make sure that whatever I fitted did not stop that being operated.
I used a combination of two fitting kits (2 & 5) from a US company called SeatbeltPlanet …...who I also used to make the belts. Additionally I bought two Carabiner clips with a 150Kg breaking strain plus some extra nuts and several 50mm x 50mm Thick Plate Washers designed for seatbelt mountings from a motorsport supply company here in the U.K. I initially decided to use SeatbeltPlanet because they could make the belts with webbing that matched my car’s Ivory White interior, but knowing that their fitting kits would be a good match to the belts anchor points also helped.
The lower mounting holes on the car were made using the instructions that came from SeatbeltPlanet plus a bit of common sense (i.e. checking the underside of the floorpan for pipes, wiring, etc. before drilling through it). Like the guy from the internet I used the pair of triangular brackets underneath the rear deck to locate the upper point of the seatbelt using the carabiner clips and the ringbolts from the #5 fitting kit. In order to get everything to fit under the rear deck I had to cut a slice out of the circular thick washers which went behind the brackets (also got from one of the fitting kits). But I also used the length of the ringbolts in order to add further washers that were large enough to go above the metal lip which is goes across the car just behind the brackets and which is a just under the rear deck. My thoughts were that this would add some extra support for the triangular brackets.
The final bit of work was to cut a longer and deeper notch into each of the quarter panel trims so they didn’t foul anything. I managed to save and re-use the edging and since everything is hidden by the drop curtain the deeper cut doesn’t notice anyway.
Hopefully this and the pictures are of some help.
