idler pulley

The 907 flail mower I got doesn't have any of the idler pulley bracket, arm or spring. I've bought a new belt and pulley. My question is can I skip the whole spring and arm and just make an adjustable bracket for the pulley to mount to. I would make it with slots to manually adjust the belt...

I have a 60 inch mower which I thought was going to need a new idler pulley so I have on on hand. Today it came off just as we finished mowing. I cannot figure out how to keep the pulley on the mounting pole as I have the keeper pin but see no grove to put it in on the pole. I suppose I could...