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BA Cylinder Heads - Boss 260
As of July 2003 build dates, BA Boss 260 engines underwent a running change to their configuration which included the implementation of fully threaded spark plugs and enlarged water cooling passages in the head gasket.
The fully threaded plug can be used on both early and late configurations as can the later head gasket but the early head gasket can only be used on the early model heads and the short thread spark plug is NOT to be used on the later configuration head.