Thanks everyone for the advice.
I got most of it apart, actually everything came apart very easily. I haven't pulled the hub out yet but I have taken the front idler assembly apart to address some issues there. The idler has always been a bit out of line and I did replace the actual wheel a few years ago as the machine came to me with a section of the flange missing and a welded together axle shaft. Someone probably rammed the idler into an immovable object more than once as the rods through the springs are bent and one is smaller in diameter than the other (OC3?). Also I will take this opportunity to rebuild or replace the rollers.
As far as the sprocket, it's a mess. Fortunately I have a good spare. After a good cleaning it's easy to see why it would never stay tight. The holes for the studs have been welded to eliminate the cone washers and then ground out with a die grinder so that the sprocket would fit over the studs. Calling it a "hack job" is giving it too much credit. Work has stopped for now until the rain goes away.