Here is another take on Larry's bolt head retainer idea (I welded on a curved piece of steel rod) with the application of a plain pin and clip to retire the circ-clip style pin (the proper sized pin from my junk box just happened to have a hex shaped head).
The next problem you may encounter is the new dust boot on your master is a too tight fit in the hole. Here's a pic of some junk parts and how I reduced the diameter on a bench grinder very neatly, no tears, no cuts.