If it's the same Ideal that's on our 53, as noted, the big nut and washer is all that holds the drum in position. Obviously, over years, it is possible that the drum has siezed to the shaft. However, frequently the clutches between the drum and wildcat will sieze to each other, making it where you can't remove the drum because there is a pin that holds the wildcat to the shaft. This happens because commonly folks tighten the nut to lock the drum/wildcat together and never release the pressure. Over time, moisture gets into the clutch plates and expands them and locks them together, making the drum/wildcat into essentially one piece. The drum has to be removed first (taper fit to the shaft), then the pin that holds the wildcat to the shaft.
SO...remove the nut and washer. Then with a heavy rubber or rawhide hammer (or a small sledge with a block of wood to protect the drum) strike the drum sideways at the top EDGE. Usually only takes one blow, not all that hard, to release it but maybe a couple. You may see it pop vertical a fraction of an inch as the clutches separate and the springs push it apart.
Pull off the drum and you will see the little keeper held with a 1/4" (or thereabouts) pin that goes through the keeper and shaft. Then you can pull off the wildcat. It would be a good time to replace the springs and clutch plates before putting it all back together.
Good Luck!