Are Postwar Lionel 042 and 022 switch machines interchangeable?

Yes, but if you put an O22 switch machine on an O42 manual switch, the automatic non-derailing feature will not work.  

Thanks Dan. Good point, on the auto non- derail. I wasn’t sure of the 042 functions, but they look cool for a lesser used siding.  

 I guess if I switched an 022 machine into a 042 switch track, I would have to have adjacent insulated tracks wired back to the switch machine. 

I also like the O42s for the same reason and in places that are reachable and space is limited.  

042's are a great option for a multi-track yard, where the operating levers can be reached easily. They especially look good if the curved part is cut back by 15 degrees, which reduces the track spacing considerably.

Rod