Our two dampers for these engines are set up for 4-bolt accessory pulleys. If you have an earlier engine with 3-bolt accessory pulleys, you can use this damper, if you switch to 4-bolt pulleys. The damper is supplied as a neutral balance damper and the kit includes three different counterweights. One counterweight is for the 304 engine, one for the 360 (also fits some late 401's) and one is for the majority of 401 engines. The included instructions provide complete information for which counterweight to use with illustrations of the various types of dampers for identification purposes. Both of these dampers include 60° of clear, easy to read timing marks along with engraved marks every 90 degrees on the damper circumference.