How well you can oc your 8600K is determined by your luck in getting a good chip.
Since you have the cooler for free, go ahead and try it.
Keep your stress test temperatures under 85c.
The processor will throttle or shut off if it detects a dangerous temperature.
That is around 100c.
Do not expect too much.
I expect you to barely run the 8600K at stock.
Insure that you have good front intakes to feed any cooler you have.