It sounds like you may want to compare costs of new CAT, aftermarket, say Berco ? or similar, for complete new.
SO the chain is stretched, needs sprockets (non segment type?)
You have not run to destruction yet, if you have rail height or enough, that is a small track, if you check the cost with a track shop, you could compare getting the pins turned which may give you more room on the adjuster again, tighten up those tracks and get those pins to sit back near the root of the sprocket, it is possible that you won't have to change the sprocket, but I am not totally sure in that case when done you won't experience accelerated wear, or a higher wear rate than normal or in normal conditions, I know the pins can ride back closer to the root of the sprocket teeth once the chain is tighter, not an expert so don't quote me. It sounds like you have options, and good that the pin bosses have not started hitting the roller flanges, what a bumpy ride, in that case some cut off the flanges, again not an expert on that.
Decent rails, or enough to get a few hundred maybe towards a 1000 hours, pin/bushing turn, tightens the track, then the pin sits where is supposed to in the sprocket, you have good pads, idler, rollers, carrier roller, for the use you describe, take all that and compare to replacement,CAT after market.
At least its not a large tractor where the costs, are so much more, last time I brought a D8K to the CAT dealer for undercarriage work, '93 it was $30,000 + and that did not include new pads, it was run to destruction, I mean pieces falling off as I unloaded it from lowboy, the yard guy, (union too) would not touch it, we always unhook, unchain and they unload, UAW rules I thought, it was the first time I ever saw anything like it, looked like the old Munsters Episode where grandpa's hot rod was leaving a trail of major parts and components. Yard guy was afraid of tossing a track, I got it off and parked before that happened.
I do know that some combinations of the above can work and other times you may accelerate wear, whereas you may want to do a better job, and you can replace more, still save a few bucks and renew some hours on those track frames. A good undercarriage person could measure all components, compare against new and really tell you where you are at and know what the options are.
It does not make sense to replace some parts, and say your sprockets are plumb wore out, run on those and still have sloppy tracks that could come off or wear other components drastically, you don't save there, unless you can run awhile to destruction, not sure on that older D3, must be a pedal steer, need a good size puller or special tools to take a sprocket off if not segments.
Places I worked had a lot of these size tractors, its amazing at how the undercarriages wore, between operators with good and bad habits, various soil conditions and so on. Most of these guys were grading, spreading topsoil and so on, running like heck, 1200 hours or so before some U/C work was needed, don't recall all the particulars, but some guys could trash them in a seemingly short amount of time, given the expected hours from a tractor and U/C.