Well... I did it. I put the 86's into peroxide for 3 minutes, then a clear wash and, voila:
Before:

After:

I must say I'm pleased and now they look great in my album and (as I said before) no one will care that the gum has gone until I'm gone!
(One was hinged, I discovered.)
I will wait a while before treating the 85's. That gold one does have a certain je-ne-sais-quoi.