Hi there! The TSM shows cast rockers oiled through the rocker shaft mounts and single valve springs (no inner springs). The heads I removed have stamped steel rockers oiled through the pushrods. The heads I am building have the oiling ports in the shaft mounts. My question: is one system better than the other? Single or double springs? I'm swapping heads because this motor blows head gaskets every two years, always at the long rear water jacket ports, even after decking. Thanks!