I have the 60mm and don't use an external finder at all, just the whole viewfinder window and it works fine. The VF window's full view is just ever so slightly smaller than the 60mm's FOV. If you have a piece of ground glass, or even some Scotch tape, you can check it against the film plane.
Yep thanks for that .. I'm finding the same to be true here, so I think I'll be fine without the external finder. Loving the lens ... I swear, these systems have to be the most-ignored biggest bargains around