AMC V8 engines are externally balanced and are engine specific. All AMC V8's have their own flywheel. I.E. a 360 flywheel won't work on a 304, the same with a 401. Very technically each flywheel should be balance to each individual engine. I can see it now, Why did he say that and where is the technical article? When I needed a flywheel for my 360 two different shops, Don's Hot Rod and another I can't remember the name of said essentially the same thing, "To do it right you need to buy a blank and have a machine shop balance it to your engine." The very thought of how much that would cost scared me to death. I got mine from Rob at Willys Works, it works and I'm happy with it.