Over the last few years, I've refurbed a ton of Peugeot mixte's. Almost all have had either a RD with a broken pulley, a FD with a cracked clamp, or both. I've hung everything on them from cheap Shimano derailleurs taken off of Magnas and Roadmasters, Falcon derailluers taken off of Huffys, and mid to low end Suntour Hero's, Sprint's, and 7's.
Bottom line is that they all worked, and in most cases worked better than the Simplex stuff. Friction shifters don't really care what they're pulling on, so as long as the RD matches the chain, you're jake.
"Love is not the dying moan of a distant violin, itís the triumphant twang of a bedspring."
S. J. Perelman