The models 1891 and 1892 .22 levers were blued frames, with CCH as an option. The models 1897, '97, and 39 were all casehardened throughout their production. If your 1897 or '97 marked Marlin is blued, it wasn't done at the factory.
Hammers, triggers and levers were cased on early 1891 and 1892 Marlins. This is often missed when someone restores one of these early Marlin .22 levers, so they blue everything. Another dead giveaway that it's not factory.
Darn! I was afraid that was the case. I have a beautiful little 1897 in the 2060XX range with a very nice "restoration". The bore is perfect and whoever did the restoration made it look like factory. It is a great little rifle.
