Thanks a lot for your exhaustive suggestions and info!
Now I realize that T60 is not as easy as it seemed to me in the beginning
Yes, I made some primary cleaning of external panels and knobs(pots), but didn't make it inside yet. Thanks for pointing me out there.
The belt I ordered at turntablebasics.com marked exactly as FM25.75, so that I expect it's the right one. It's clear for me how to adjust QL off mode, I read the manual carefully.
My strobe discs are quite sufficient for the task, I realized that yesterday. As to the motor pulley, I clearly saw, that there's no way to apply the approach mentioned in the docs, once it seems like the belt embraces the spindle itself. Please, correct me if I'm wrong. Anyway, you say that all the stuff had been thrown away...
Being optimistic, I hope that the proper belt will make the trick.
And you're right, QL off mode would help in adjusting the RPM as a viable resort.
Fortunately, manuals are avalable here at VE, so that I may consult them along my way forward.
The headshell is the stock one, it's coming in a couple of days. My friend just forgot to attach it to the arm. Once the shell mount isn't standard, I doubt that I can find anything similarfrom the source other than HK.
And there's one more question. I found that the platter mat is hard and hazardously fragile. Would it be good to exchage it with a new one. What kind of material is best, cork, sorbothane, or acryl? Acrylic ISOMat is available on eBay, and its price is quite affordable.
Thank you again for the great comments and multiple source references on the topic!