I have a 1990 Davidson Impulse with a Shimano 600 Gruppo. My chainrings are 52 and 42 and my biggest cog on the 7 speed rear cassette is 24 teeth. My goal is to get the lowest gearing that I can reasonably get to flatten out the hills of Austin,Texas for my 52 year old legs.

What combination of cassette and chainrings could I get that would function with the Shimano 600 deraileurs?

Should I change deraileurs? If so, what kind should I get? Could I find a good used set on ebay?

Could I change to a triple ring in front? Would that make a lot of difference?