On my '69 PX-10, I had very good luck for thousands of kilometers with the original Simplex Criterium rear derailleur shifting a 5 speed freewheel. I suggest that you stick with Simplex (maybe upgrade to an all alloy model). I hope to pick up a very weathered PA10E today and if the Criterium Derailleurs are too far gone, they will be replaced with Simplex.

A bolt on Campy hanger will move the derailleur outboard and while it will work, it will look bad.

Wrt stem and bars, they are a safety issue and I rode with a sanded down ITM combo.