With a 66 GTO Hood you have a bit more clearance vs the normal hood. Not much though. Pretty much the same as a 65 Hood. Mike (MJM421) ran a Performaer RPM on his car with a 455 engine and liked it a lot but also mentioned that he had minimal hood clearance for a flat filter and had to use a dropped base air filter. Still not much clearance.
I also remember him saying that the RPM manifold worked very well on his STREET CAR (Mike drives his stuff) with a 850 carb. Might have worked slightly better with more air cleaner filter area above the top of the carb. The car would run faster at the track with the air cleaner off. So the RPM manifold in my opinion is a very good street manifold. I have run a couple of them over the years. That being said, I have also heard good things about the Kauffman Racing "Northwind" intake manifold. More hood clearance, very good power capability. Holley bolt pattern.
Tom Vaught
I believe that "JIM" at this business
http://www.centralvirginiamachine.com/400resto.aspx sends stuff to Pontiac guys in Europe often.
He could easily get the intake from KRE for you and send it to you.