Phil, I think this may indeed be a pretty rare model. The outer tubs seemed to have been a weak point for these models - in a previous thread, Fred (blackstone) in MA had mentioned that they were often replaced completely. Blackstone didn't seem to be a hugely popular brand; I'll guess that they concentrated on the east coast since the manufacturing plant was in Jamestown, NY. I don't have any other Blackstone machines (so far... LOL) and you never know, the matching dryer may just surface one day! I know there are a few of the older (50s) Blackstones out there among the collector community and I think there may be a set of the 70s version, badged as Hoover, out there somewhere.
And that agitator is definitely huge! It makes for some good rollover, though!!