Don't get too hard on yourself, Phil.

Dealing with aluminum is always a PITA. It's very soft and, if the steel fastener doesn't want to release, the aluminum is going to give. Not much you could have done about it. Sometimes you can put some Kroil on it, or heat it, but, aluminum is always difficult when attempting to hold a decent torque.

It's a decent material to work with, but, never should have been used as a cylinder head in order to save 30 lbs.