In the 4" stroke MP has a cast steel so it is stronger than a cast iron piece and they have the forged steel is rated at a higher HP
ie} both are steel as apossed to a cast iron type.
I have no idea who makes them for MP so this is proberly of no help to you


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VP of the MPM in New Orleans
73 Dart Sport 340/ 70 challenger vert. That may still get built, If I live long enough