The car is a 1964 cutlass conv. Its a 20 plus years old project I didn't take apart. I bought a RC645K support kit from Fusick which some what resembles the original. The service manual showes the square pad sitting on top of the frame horn with the small diameter round extruded part of the pad pointed up through the core support and the donut on top of the core support frame. The last owner had the core support sitting directly on the frame horn.
I think the square pad with round extruded part goes on the inside of the frame horn with the extruded part sticking through the frame and the donut on top of the frame under the core support.
I need help from someone who knows the correct assemble sequence.