After all that experimentation with Cricut masks, I decided to press forward with decals for 622. They were included on the same decal sheet as the flat car decals from Precision Design, and went on beautifully. I was glad I’d included an extra copy of the decal for the tender rear because I did indeed spoil one due to the steps. The left side of the tender also has a small amount of roughness, perhaps from insufficient gloss-coat (?); it looks worse with the reflected light for photography, and so, I’m hoping the Dullcoat will improve it.
There is nothing quite like lettering to make a model start to look real!