And some instead of the weight have a wide groove in the face of the inertia ring about half way around.
Of the two types I would use the weighted kind. The weight is directly attached to the crank while the other one has the weight isolated by the rubber. If the inertia ring moves it will throw off the balance of your motor. Not much chance this will happen but it could.
http://www.moparts.com/Tech/Archive/smallblock/5.html
Chuck
