I'm sure NOT liking this.
I'd say that heating the head with a small propane torch then whacking with a hunk of wood and mallet on the exhaust & intakes SHOULD pop it loose.
If you have two mates available, get one to hold, one to whack, and one of you hold the torch. If you've a 3rd mate, have him twist on a screwdriver whose tip is only slightly wider than the gap between the head & cylinder fins (in other words, it slips in easily in the horizontal, and only starts to bind once the flat starts rotating to vertical). NOT pry, just twist. Preferably a square-shank screwdriver to that you can twist it with an adjustable spanner to get some serious leverage on it. Shouldn't be any risk of damaging fins.