Thanks for all the helpful responses.
I've always instinctively run away screaming from anything Simplex, and my instincts seem to be confirmed by verktyg.
To be sure, the actual derailleur I am considering is all metal construction; I have no interest in Delrin as a structural material.

In answer to some of the questions, I don't know the year and model of my CILO; that information was not provided when I purchased it,and it had been repainted and evidently had several of its components upgraded over the years prior to my acquisition. Anyway, here is a current photo.



What is behind my question is, my CILO is starting to grow on my as a regular commuter bike, and I'm thinking of upgrading the crankset from a traditional 42-52 double to a triple; and I'm doubting that the NR RD has the required wrap for say, 36-22 to 52-19, i.e. 13T of wrap, not accounting for shifting errors, which would extend the wrap requirement to over 30T, in the worst case.
Further background is, apart from consumables, I've kept this build almost 100% European; only exceptions so far being low profile components like the seatpost and the freewheel.
So there you have it. I have a Crane GS waiting in the wings to handle the chain wrap in the mean time until I figure out a cost-effective European derailleur for the job (grail RD being a Campy Rally; but I don't expect to find one for a price I can justify).