[sbjornda]

Yes, the prism needs to be coupled to the lens aperture lever or the mechanism will not engage and thus potentially snap the coupling chain

That's only true for the metering prism, correct? I believe the OP said he had the non-metering prism.

The prism is generally only removed to facilitate cleaning of the focusing screen.

Or to switch between prism and another finder, e.g. Waist Level Finder or Chimney Finder.