Sometimes I have an unresolved externals problem when calling some functions from engine - so far the only solution I found was to copy body of unresolved function from source to my project. This often spawns more problems, because this function body uses some other unresolved functions etc, ad mortem defaecatam. The example of this behaviour is with functions from StaticMeshBuild.cpp which includes internal methods of UStaticMesh class.
Long story short - is there any method to tell MyProject.Build.cs makefile to include some .cpp files from Engine into build? And yes, I use PublicDependencyModuleNames, I’m not that stupid 
Also trying to use ENGINE_API freaking EVERYWHERE were unsuccessful.