Does anyone know what the tabs were for that were punched in the floor and covered with tar?I found them in the back seat foot area and under the rear seat.The factory sure covered them well with 1/4"+ of very hardened tar that I had to chisel away.

I have often wondered about the very same thing. Very interesting and does anyone have any guess's. 

Does anyone have any ideas what those tabs in the metal were on the floor on these fifties GM cars.