Or, I can use a Huret claw to mount the Huret derailleur, without modifying the dropout - true? I'd like to not modify the hanger, ideally.
On the cable pull issue - if the Huret derailleur needs more cable pull than the Simplex derailleur, but the Simplex bar end shifter actually needs a demultiplicator to work with a Simplex derailleur, then I'm speculating that the Simplex bar-end shifter could work with the Huret derailleur sans demultiplicator - sound plausible?
I looked through a book of old (70's) race photos, and do see a few racers using bar ends.