The only difference between the late '32 steel oil pan and the '33 pan was the placement and orientation of the die cast fitting for the dipstick on the left upper center of the oil pan. In other words, the insert plate is the same as the '33-'34 pan and snaps in place.
There were three versions of the insert plate used with aluminum oil pans, all of which were held in place with screws as Sheldon indicated. The first was for use with the first version of the oil pump which had no pickup tube (the oil entered the pump from the bottom of a unique pump cover) and therefore had no slot in the plate for the tube. The second was also for use with the early oil pump, but now had a hole in it for the oil dipstick to pass through reflecting the relocation of the dipstick from the right rear side of the engine block to the left side of the oil pan. The third and most common had the slot required to accommodate the pickup tube that was added to the oil pump.