you just described the seat slider mechanism for my 1935 chev standard series 3 window coupe.
At the very rear of the metal piece under the side wood frames is a U channel that keeps the seat sliding straight forward and back.
Mounted back there on the floor is 2 white cast metal pieces that the U channel slides on, this keeps the back of the seat bottom anchored to the floor. If they are hooked up it is impossible to lift the seat bottom.
Because your car is a cabriolet model and made by FISHER BODY , same as my coupe , appears they use the same parts by your description.
mike