I believe the issue with the Ampico B brake drums may be more with
the finish of the material and not the material itself.  Many years
ago I commissioned several "play brakes" (the ones on the supply spool
axle) make from aluminum, but with an anodized black finish, which is
very hard and smooth.  There's been no problem in 20 years or so.

This option is probably still available to Tom for the newly fabricated
drums.

John Grant