The 389 heads did not use guideplates, and did not need them due to the tight pushrod guide hole in the heads. If you want to use guideplates, you'll have to pull the heads and machine the stud bosses flat and co-planar: The 389 stud bosses are in the as-cast condition, so guideplates cannot be installed unless you machine the bosses flat and tap the holes for screw-in studs. With this all said and done, I'm not sure that you'll really gain much practical benefit from the guideplates, since a 389 with 093 heads is not likely to see power gains beyond 5800 rpm, making guideplates of little, if any, benefit.
Lars
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