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Stock ratio on the SBF is 1.6:1 and there are 1.7 and some 1.72 ratio rockers available. If your existing heads use rail style rockers(the tip has skirts to keep them on the valve stem) you either need to replace with this type or add guideplates... which is a bit more involved because of the push in studs of course. This usually means a trip to the machine shop and if that's the case simply substituting a newer head or a set that have already been reworked is the beter way to go. All late model SBF heads(from about 1978 on) use pedistal mount rockers which don't need guideplates and are therefore easier to add rockers too, but in most cases the combustion chambers are larger than the early heads so you could lose some performance. That's not a certainty though it depends what heads you have right now, the casting number would tel the story and that can be found on the head gasket side near one of the intake ports.