John,

Well spotted regarding the 81.  I agree it does look something of a hybrid.  Maybe wartime and they were just putting sections together as they had them available and it was not too citical for work in the factory. Do they look like over size rear tyres to you?

Here are a couple more illustrations from the factory.  The first shows the bright steel shafting mill with furnaces in the background.  The second shows them drop forging gun parts.Looks like it was pretty hot in that factory.

Wonderful artwork don't you think?

John