I exported a bunch ob boxes and tried them in game.
It was allot of guesswork, but i saved the one closest to one Block as a template.
Its not a 100% the right size but very close.
I have a .blend file and can upload it somewhere if it helps.
You can adjust scale right in the editor or create a simple cube with 64x64x64 size.
64x64x64 in blender units?
OpenGL units. They should be the same in Blender
Thanks man!