That 7,7 is a true ratio,calculated using deck hgt, piston valve notches, head gasket and head cc.
My 1966 390 GT was supposed to have a 10.5 ratio from the factory, when calculated it turned out to be around 9,9.That engine was " factory sealed" meaning I was the first one to open it after 1966.
-66 Fairlane 390 GTA.
-70 Torino GT originally 429 SCJ DragPack.
-80 Fairmont Futura Street 393 11,05/ 125mph.