Schwinn made the best bikes in those days! I had a black one like this but it didn’t have the shifter. It was not easy to learn how to ride on a dirt street with an overzelous step dad making me keep doing it until I get it right… I don’t remember exactly how much blood I spilled but it was enought that I remember my mom being upset at it
Those are on the frame I believe, road bikes had them there in the old days
My 80s Miyata road bike has frame shifters for its 2x transmission.
To go with the style, shift lever should have been one of those:

I want this style shifter on my trike now
Can confirm, I was there in the old days.
Schwinn made the best bikes in those days! I had a black one like this but it didn’t have the shifter. It was not easy to learn how to ride on a dirt street with an overzelous step dad making me keep doing it until I get it right… I don’t remember exactly how much blood I spilled but it was enought that I remember my mom being upset at it