A Ries head does not pan on a Gitzo tripod head simply because the manner in which it pans in a Ries tripod is to loosen the screw that holds the tripod head on the tripod with a bolt under the tripod head base. The Gitzo tripod bolt is static and as a result, when you put a Ries head on a Gitzo tripod I believe that you sacrifice the ability to pan.
I use a Bogen 3039 three way head for my 8x20 Canham that weights a bit more than your 11x14 and it works great. For and aft leveling bubbles and a quick release plate system that holds great. Having three arms to control fore, aft and pan directions is very nice and they lock down solid and secure. This is what I would recommend if you cannot find a way to pan with a Ries head.