Its supposed to stiffen the block "which I question when it comes to the 351c block because of how the water ports sit " And it is supposed to dampen vibration. I question if you need to use it in your application, My next 351c will be a full Hardblock alcohol monster and I wont even consider that fer another 5 years- You SHOULD have the rotating assembly balanced-

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dude,do a poppa-willie!