G,day dude it looks like your going down the same road as I'm on and must say going by the serial number that bike is from 1981 at the oldest, certainly early 80's to mid 80's.
I would say it was one of Schwinn's lower end models on the same level as my Ricardo featured on this site.
But thats no reason not to put your hart and soul into rebuilding it and one great thing about these old 1020 steel frames is there very robust and built to last they also fit 700c, 32c cyclocross tires for extra ride comfort if you wish.
I've got a little known trick for refurbishing all your chrome and metal and alloy parts nuts and bolts etc. etc.
1. A nice big plastic tub with a lid, big enough for the whole crank set as thats about he biggest thing you'll put in there.
2.Fill it with kerosene so all your parts are totally submerged for a day or two and give them a good scrub with a stiff brush when you take them out.
3. If you have a air compressor thats a big help if not just wipe them down with a rag and dry out a bit.
4. This is the big trick where the real results come from, fill your tub with Brown Vinegar you can buy this in Two litre containers from your local food store. Totally submerge your parts and leave them for 24 or more hours.
5. When you remove your parts from the tub rinse them under a tap and use a basin kitchen cleaner here we have a product called Jif cream cleanser or use similar and scrub them with a tooth brush and rinse.
6. Its good to blast all the water out with a compressor or just spray them good with a water dispersent like WD40.
If you follow all this you will thank me and you can repeat the brown vinegar trick as much as you want but usually once is enough all your rust will be gone parts will be new again.
Good luck with your rebuild I'm keen to see your progress.