No, but a 318 head will have the same effect on a 273 as it does on a 318...
the 66 - 67 273/318 head will keep your compression closer to factory specs than if you put an open chamber head on it... If you put an open chamber 273/318 head on your 65 273, you will drop compression about half a point because of the larger combustion chambers.... If you put a 66 - 67 273/318 head on the 65 273, the compression will be close or the same as it was from the factory...