yes you can put the hub in a lathe..and turn the old drum aut,,and find a drun from a small car/auto trailer..turn it dovn to fit the hub..it must be heatet up and the kold drum put in as a schrenk fit..and some safty threads drilled in to fit som safty schrevs 3 or 4 to ekstra safe
i bayed a reserve hveel in germen e bay,,but it have almost same defekt...so be ekstra care baying used stuff...the old 550 hub fitts..but later 550 have a different brake plate..so go for a 500 for safty
my plan b..are to frit a small disc brake..and build a adapter to press in the old hub..but it are hard to find a small nice disc...750 f disc are as big as hell