It’s been a while since I worked on my Vitessa, but it seems from your photo that the cam should rest on the silver arm right below it that you see in the image. So the solution would be to move that silver piece that you can see through the hole up and then move the cam towards you (as seen in the photo) so that it rests over it.
I can’t guarantee that this is correct, but a way to check would be to move the lens back and forth a little bit (as you would when adjusting the focus; you can do this by placing the focus wheel on top of the round hinge and using it as if the camera is assembled) and verify that the piece I mention moves with it. Since the cam only translates the movement for the rangefinder, it should follow whatever motion is produced by the lens and the focus wheel.
I hope this is helpful. Would you mind posting your results here once you try again?
