They tell you to leave bolts A and D on slightly to prevent the head from flying away, then in the same breath they tell you to beat it with a mallet (but softly...) to get it loose. I do not think the heads differ in how they separate from the motor. Can you get a mirror back there to check? Have you tried a mallet? I wonder if the heat on that side, which is higher than the other side rear and both front sides, is making the difference.
Heads off with motor in takes courage.