They would have put it together the same way it would come out.. everything can move on the shaft, when new and not rusty the brake disc would have just slid on the shaft, as would the bearings. you just put the shaft through one side, put the brake disc on and put it through with the other bearing on the outside. there will also be a key way in the brake disc.
When that happens I use a multitude of screwdrivers, pry bars and cold chisels to wedge it back across the shaft. if you tapped it one way it will go the other, the problem is getting leverage on it.
