To all: Any help would be appreciated in confirming what flywheel I have. I think I have a flywheel for an internally balanced motor but want to make sure. This is what I think I know about this flywheel can anyone confirm if I am correct ? 1 The casting number pictured is used on (both) internal and externally balanced motors 2 It is a 130 tooth 6 bolt flywheel and is used on big and small blocks My big question is this, What are the 3 drilled holes that are pictured ? I have been told that for an external balanced flywheel that there should be 3 large circular areas taken out further in towards the center away from the starter ring. I have a vibration that starts a little over 2000 RPM and seems to fade way above 3000 RPM. It is a small block LA Motor with a mild camshaft backed up by a 833 4 speed trans. I have checked it it in all gears and speeds and seems to come from motor only and not the drive train. I have tried everything I know to resolve this. Any help would be greatly appreciated.