There is a big difference between the 1949 and 1950 622. There were illustrated parts manual for both of them. The 623 had a revised magnatraction and eliminated the bell. Most of the rest is the same as the 1950 622. As far as I know there is no illustrated parts manual for the 623, just a parts list showing the different parts from the 1950 622. All of this is in the Olsen online library of parts manuals. There were three Lionel diesels developed late 1940s, 622, 2023 and 2333 and they share a lot of parts.