"...assuming the shutter is the typical reversing kind (moves one direction then the other on alternating frames)..."

Polyglot: a reversing focal plane shutter? I don't believe I've ever seen one. All FP shutters I've dealt with over the past 40 years have opened in only one direction. Open the back on a Leica M, set to 1 second and fire -- you'll see a curtain release (left to right IIRC), then the second shutter release to end the exposure. Advancing the film and cocking the shutter returns both curtains (now closed) to the left side, and it begins again. I've never seen an FP shutter where the two blinds alternate from side to side -- how would you tension the shutter?

I'm just trying to learn something new...