The frame is held on the sliders with 4 bolts that stick out the top of the sliders themselves. They are in the recesses on each corner of the frame. These are studs not bolts, so you need to clean them and use PB Blaster or similar on the threads. They are easy to break if you don't. Since you have a 1950 the seat frame is also held on the sliders with small bolts and a clamp on each side for the cables that runs through the back of the frame. These are 1/2 way down the frame on each side. If you look at the picture you can see the bolts and the clamp assembly on the side of the seat frame.

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