IMO any FG conversion that does not use a proper FG hub, or a properly FG converted casette hub, is dangerous. The torque transmitted to any FG converted freewheel when slowing down or stopping w/o brakes will try to unscrew the freewheel from the hub and without a lock ring as, used on a proper FG wheel, it will probably happen eventually. The same is true with installing a FG sprocket on a regular freewheel hub that does not have provision for a left hand threaded lock ring.