The knee lever pedal on my cabinet is located on the right side too (for the 401A Singer), but I think your cabinet is missing the back board that will support the sewing machine and it's weight.
These cabinets were designed to "tuck" your machine in when you were not using it or for storing. The sewing table area folds down or flaps down and you tuck the machine in first, flip the sewing area down while the machine is already tucked inside the cabinet, then you'd screw off the four legs.
The legs on my Singer cabinet screw off, making the whole ensemble (machine & cabinet) easy to store when not in use.
Sometime ......(not now, very busy night, but......) I'll try to take step by step photos of my machine/cabinet explaining how my machine packs up and stores.