I had a hell of a time cleaning some old head gasket material off a head on a friend's /6 not long ago.
What didn't work
: acetone, Goo-B-Gone, heat, razor blades, wooden scrapers.
I think it helps to apply it to a warm surface. Let it sit for maybe half an hour. Try it on an inconspicuous spot first. I was cleaning off baked gasket sealant on an aluminum head. Wouldn't think it would damage chrome, but better to check.