Jegs is on crack....What they say doesnt make sense...what it should say is wont work on 2002-2003 5.9 Magnums because they had one piece cast pulley/balancer combo, which would work, but only if you got a removable pulley from an earlier magnum.
The deal is LA360 and 5.9 magnum use different weight due to LA having heavier pistons. You cannot use an LA 360 on a magnum because balance would be off. We use PRW balancer which is the same piece as PP is selling, but it comes with 3 weights so you dont have to but extra one. If you are using LA V pulleys, keep magnum balancer and run your V pulleys on it....no problemo.