I have the following Schwinn that I'd like to fix up a little bit to enjoy riding but I need to know what I have first. I believe this to be a 1989 or 1990 model year Sprint.

Also, if anyone could help identifying some of the components shown. Simply as stock (originally manufactured with the bike) or aftermarket. I'm not going for a hellbent OEM restoration or anything, I'd just like to figure out what were original components and what are not when I go to service/update.

Thanks for any help you may be able to offer.

Anyone? I guess my bike is too ancient for anyone to remember.

Looks older than you guess. SR crankset. SunTour shifters/RD. Original(?) Schwinn-approved rotten tires.
Rusty FD, headset, pedals(!!!).

I was perusing some forums/websites about swapping gearsets and wheels, etc. and it seems there are two main spacing on the back fork - 120mm mostly in the old stuff and 135mm in the "new" stuff.

Can this be measured on the bike? Measuring on the bike I'm eyeballing with two straight edges about 130ish mm.

You should be able to get a reasonably accurate measurement with the rear wheel removed.

Have you tried googling schwinn sprint images? Look for similar "schwinn" graphics on the downtube.

There are many more "standard" measurements then 120 and 135mm. See here: https://www.sheldonbrown.com/frame-spacing.html for details on how to measure, etc.

Note that I think trying to do any large-scale parts upgrade on this bike is going to be more trouble then it's worth.