You might find that the rear hub takes "standard" old-style freewheels, but you're limited to 5-speed unless you put in a longer axle (not out of the question) or find a "compact" 6/7 speed freewheel (likely scarce as hen's teeth).I suppose you could put in a new BB cartridge and have 3 chainrings, but the BB standards were the least "standard" of anything back then.
So now, I have a nice, smooth-riding vintage steel-framed bike.
The old song goes "the best things in life are free".. I have had two bikes which I found in the dumpster (rubbish bin here in Australia).
I'm an adult that is new to biking due to a triple whammy of a childhood aversion to effort, my family moving to a town on the side of a mountain with steep roads, and my bike getting run over by a neighbor (I gave up riding around age 10). shifters I'd start replacing the shifters for indexed ones. but will require a lot of research to match them with the rear derraileurs (the gear shifting thing on the back). Wheels if it has Sealed bearings in the middle of the wheel you are fine.
I didn't buy another one until my wife got me involved riding with her. He's had it in a storage unit for at least fifteen years, though possibly more. Another option is to just keep the ones you have (friction shifters) and feel the gears changing.
With some time and elbow grease, and sometimes a little bit of money you can restore a bike which was destined for the dump into something that is fast and fun to ride around.
This instructible shows you how to restore a dumpster bike - in this case a 10-speed road/touring bike.
Changing your chain requires changing your derailleurs, both of them, preferably, although you might get away with leaving the front derailleur.
If you spend the money to go that far, a whole new bike kit, which should be possible to make work on the frame, isn't that different in price, depending on your choices.
I have a 40 year old Bottecchia (entry level model) that I took for ride yesterday after letting it sit for 20 years. It originally came with low end campy components but I replaced the crank and derailleurs with inexepensive Suntour and had the wheels rebuilt with Weinmann Concave rims and the brakes are center pull Weinmanns.