A flywheel holder can be made from a section of steel bar 30mm wide and 5mm thick available from hardware stores.Drill two 10mm holes and one 16mm cutout as per picture and use 10mm thread



If you remove the thread nearest cut out and file the end of the remaining thread to fit into one of the holes in the clutch spider the cut out will fit on the rear shocker post and you can hold the spider whilst tightening/loosening the spider nut
This was posted on old database .Although the old forum database appears lost the ideas,fixes, pictures of rebuilds and comments are still there on individual member's computers and could be re-inputed to rebuild the database.
This is a start
Grandpa