Wufnu, No, it's not necessary to cut off the crank. I had mine apart for new bearings, I cut it off with a hacksaw, the shaft isn't very hard. I then cleaned up my cut on a sanding disk. I just wanted to lose any weight I could. Some on this engine conversion forum have used an old capicator case for a plug, but I didn't have one. With the proper size plug pressed in, screws to hold it in would be uncessary thus even less weight.
Don