The GT heads are untouched and the Navi's were ported (not sure by who). You can really see the difference a +2mm exhaust valve makes, and also the raised intake ports of the GT head. The exhaust port is monstrous as well, they are the same as '00R heads.
Pics: http://www.modularfords.com/forums/showthread.php?t=19500&page=1
Pics: http://www.modularfords.com/forums/showthread.php?t=19500&page=1