In my experience turning pins and bushes on the tractor the size of a D8R is a waste of time & money.
The additional Link Group life resulting from the pin and bush turn is outweighed by the cost of doing it.
Your tractor appears to have Cat undercarriage on one side and aftermarket U/C on the other.
My suggestion would be to have the dealer PSSR out to measure the undercarriage on your tractor and produce a report for you.? It's a FREE service and you would do well to take advantage of it. Your photos with a tape measure just don't cut it.
So Cat are quoting you $20k per side. What exactly does that quote include.?
You need to know the asnwer so that you can accurately compare quotes from different potential suppliers.
For a full undercarriage overhaul I would suggest that you need to consider the following items (some of which have already been mentioned by others) in addition to the obvious items such as link groups, shoes, ilders, track rollers, and sprocket segments.........
1. Track tensioner seals and fibre wear rings.
2. Condition of equalizer bar centre and end pins/bushes, & associated hardware.
3. Condition of bogie pins both major and minor.
4. Condition of rubber bogie suspension pads.
5. Condition of steel bogie tip wear protectors - yours are worn out.
Edit: 6. Condition of Pivot Shaft, machine frame bushes for the pivot shaft, and pivot shaft seals