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It is tempting to use putty knives and screw drivers to help in lifting heads off. Using screw drivers or similar can and often will damage the edge of your block. Resist the temptation to do that. Putty knives can help in breaking the seal but remember you have valves in there and if you drive putty knives in to deep you can damage/bend them.
If the head only wants to come up a short distance once you get it broken free don't hesitate to drive it back down and start the lift again. Going back and forth and keeping it level when going up will go a long ways in getting it off.
Sometimes it is worth the expense and the wait to get one of the head pullers from a vendor.