Well, that got a lot more files to compile. I see that I changed to popupmenu.class for popup-menus in AE4, so I have to rewrite them back to popupmenu.library. When disabling that code, there is only 4 C files left to compile (and all plug-ins of course) so it's progressing nicely.
I'm on a congress this week, so porting will stall for a week, but it's looking good.