Sheesh. What a mission that was.
Tried almost everything. Some industrial solvents are no longer accessible to me, more's the pity.
Even remembered that an over-spray from AeroGuard pretty much destroyed the plastic case of a fairly expensive / elaborate piece of electronic test equipment I have, so tried that too. Not a hope.
Bushman; nope.
White Spirit; nope.
Paint stripper of any kind; nope.
Abrasive 0000; nope.
Even tried scratching the surface with abrasive to allow a better key for the solvent/s, to no avail.
Only thing that got "close" was Citri-Strip. A type of gel that eventually got the coating soft enough to be able to scrape it off. But not easily. In fact, required several re-applications. It certainly didn't bubble and blister as one might expect from a paint stripper.
Whatever it was that Winchester used was never meant to come off, but god help anybody who wants to fix a tired stock

And I was hoping to one day remove the horrible gloss finish from a Browning rifle and revert it to a much more agreeable (to me) satin finish. I'm having second thoughts about that one, horrid though the Browning is !
The next part of the saga becomes: surface treatment.
I have Danish oil, Tung oil and Teak oil.
What, in your opinion/s will be best, for durability?
It is my intention that whatever is used will be allowed to cure, surface re-smoothed with 0000 steel wool, re-coated, etc., etc., for as many applications as may be necessary.
And when it's all done, I'll post a pic or two of the effort.