I have the .91 ASP FS pulled down waiting on new bearings to arrive and I just noticed the cylinder sleeve will fit over the prop hub. It's not a tight fit. But its close enough for a grub screw to be used to attach the ring.

I wonder if I cut one down to size. Drill a hole for the magnet undersize. Then heat the ring and insert the magnet and let it cool down.
That way it should grab the magnet without the need for an adhesive. As the ring will shrink back when cool and close the hole?

The cylinder for these engines is like $6.50.

I have the FS61AR as well. The sleeve and hub don't quite fit. I reckon if I heated it up to do the magnet install I could get it fitted. They measure the same on my cheap vernier's. But they dont quite fit into each other.