Mm, "DIY" calibration of 8.5 gear is somewhat mythical. My personal plan on this is:
A. Clean all dirt, replace broken parts (so far transformer, pair of protection zeners in inguard PSU, dead NVRAM, missing knobs+levers)
B. Install missing LTZ1000 reference (already one of those ebay units on its way).
C. Carefully test and repair analog section (if needed). This item is a real deal, and if unobtanium stuff dead - can quickly make whole project worthless.
D. If all analog stuff works - assembly meter and ACAL it to my K2002 readings on 10v and 10k. This will let me check overall function, drift, noise and such.
E. In some distant future , if everything works really well - send it to Keysight for cal.
OldSchoolTechCorner
Ouch, 1.1k? Kinda steep to my liking, hope you know what to expect. Photos clearly show missing ref board. But its not the reference you should worry about (they are up for sale for little over 100$ like cakes on ebay now) but that paper sticker "Defective" on transformer. You looking at 337$ replacement if u choose to get new from HP.
I would not mind at all if you post you progress in this very same thread, as its same topic, same seller, same stripped parts!