I can send a simple test program which I am using now if it helps. It is a bit weird though as using MFC in the main app. And I still have a problem running it in wine64 ('System.InvalidProgramException: Invalid IL code in <Module>:gcroot<System::String ^>.= (gcrootSystem::String ^*,string): IL_0004: call 0x0a000012' on calling IntPtr.ctor(void*)) which I am trying to fix. So maybe a simpler one could help. Unfortunately I don't have MSVC and cannot build mixed assemblies myself.
If you have Windows and would like to try, you may be able to use Community Edition for this.