The "large head" is in each of the 2 cylinders? Any ATF? A specific viscosity?
After I received the first answer I drove accross town to my boat. Not knowing where the the "cap" was or what it looked like, I removed three caps. The third one was the right one. I wish you would have told me it was an 11/16" bolt. I wish you would have told me I would need to get the ATF in horizontally. Not easy to pour oil sideways. Advice that I would need a pump oil can would have been helpful. I do not agree to pay an additional $20 for information that should have been in the first answer.