Some people adapt S1s to S2 style chassis mounting.
And, again, the S1 chassis is NOT really bonded to the S1 body. The S1 body is actually made of two sections, lower and upper, bonded together. The chassis is laid in place and then the two sections are bonded around it. Then the chassis is also riveted to the two chassis sections in multiple places. The very ends of the rear “Y” sections bolt to the inner fenders, and, the lower section of the rear loop is bonded to the floor of the engine compartment — the only part of the chassis actually bonded.