Finding a BP-project's Character/Controller from C++ AGameModeBase

I have a project that I created as a Blueprint project. I want to use a custom Game Mode, and I’ve set all the same ::StaticClass()'s as the default game mode uses. But the PlayerControllerClass and DefaultPawnClass settings elude me, as these exist as blueprint assets. I naively tried:

DefaultPawnClass = LoadClass<APlayerController>(NULL, L"TopDownCharacter", NULL, LOAD_None, NULL);

But it fails to spawn with a warning of

LogUObjectGlobals: Warning: Failed to find object 'Class None.TopDownCharacter'