Sadly they are not, at least not in form factor. Even though many of the onboard components are the same, the layout is just different enough that I’m not convinced this would work without modification. For example the trackpad connects on opposite sides of the battery connector. Also the battery connectors are different.
I have never checked to see if a 13” board would mount in an 11”, but based on the locations of board mounting screws, I doubt it.