The RB-67 has a bayonet mount and a bellows bellows focus system, but lacks a focal plane shutter.

That didn't stop me from machining an acetal bayonet ring to which I mounted an PVC tubular barrel into which I installed a Meniscus lens.

Of course, timing is "iffy", since I use the Top Hat Shutter system.
It works.
Very nicely.
Take a look...