The measurements are the same, that's why I asked. I searched the forum for this replacement options before asking because I was sure I wouldn't be the first person to run across this Cub part number being NLA, and wondered what the replacement would be. The google machine found me the 2.12" (2 1/8") Dorman equivalent part. I hope it works, I'll have a 1957-1959 Dodge Camshaft cover in this tractor.
I found a pack of 10 for not much more than one plus shipping on feeBay, I'll have them Friday. If that works, I'll have 9 extras.