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Blue Moon Manufacturing offers 1930's era vehicles in soft metal and resin.
Matchbox "Models of Yesterday"
Matchbox's Mack is Scale55. I compared the dimensions to Jordan and Con-cor's HO version and the Matchbox model matches the HO models.
The steam tractor is also the right size.
These can be found at Internet auctions and toy shows.
Lledo's "Days Gone By" series scales out well to Scale55.
These also can be found at Internet auctions and toy shows.
Reviresco has a "1/64" line of cars and trucks that scale to 1/55.