I think that I read that the reason for the Z11's squared off valve covers was to clear the push rod guide plates .If true,then the Z heads would have had screw in studs,not pinned.Some body like Russ would know for sure.
Don I think the z11 guide plates bolt on along the top of the head just below the valve cover rail not under the studs. It’s been a while since I have seen a set of z11 heads in person but that’s how I remember them.