I've got to respectfully disagree with tubman....The early 21 stud Eddie Meyer heads have different combustion chambers to stock Ford heads....Most aftermarket heads very closely resemble stock ford combustion chambers. Sure, those Edmonds heads, that tubman prefers on account of the relocated spark plug, have a very low roof, I don't think they breathe as well.
It's the old trade off....we want to increase the compression ratio, so we lower the roof. However, the incoming fuel/air mixture upon exiting the inlet valve wants to continue its upward motion, but can't; it gets deflected by the roof. Now, if we raise the roof, that'll improve the breathing, but have the adverse effect of lowering the c/r. Or will it? Stock, [and most aftermarket combustion chambers], basically follow the same shape as the head gasket....Those early Eddie Meyer heads I referred to earlier, have a high roof, but it is narrowed, measure at 60cc, provide excellent breathing and compression. In my opinion, this design is far better than the Edmonds design. Now, if only the spark plugs were in the Edmonds location....