Originally Posted by
Metacortex
Roger what rear derailleur is on that bike? Post a close-up pic if you can.
The photos of the two bikes in this topic/thread seem to show Schwinn Approved variants of the Huret Allvit derailer.
Post-~1974 versions had a cage with extensive chain-guiding features formed out of what looked like bumper steel, so were heavy beyond compare.
Those features helped beginners to avoid damaging derailments when a rough shifting technique was used.