I'd like to see the URL that shows that because it is incorrect. First of all there is NO 1965 (or any other year that I am aware of) engine code designation for a "A/C" GTO. They do not code engines as to wether they had A/C or not. The codes designate carb/tranny combos. If you look at my previous post I listed all the engine codes for 1965 GTO's. That's all there is and there ain't no more.
Here is a Wallace URL that lists the engine codes.
http://www.pontiacpower.org/engine.htm
You will see that the YD is a 290hp 389. There are no YD codes for GTO's. I also scoured my GTO resto manual as well and could not find a YD code for any GTO engine 1964-70.