Hi guys, I just stopped by my local dealer and the tech showed me something interesting. He was doing a major service on a 360, but it had all of the seals that challenge engines have. After he cut the seals he found that the cam/sprockets were marked. The story goes is that they put the engines together and dyno them all. If some produce more,they go into a challenge batch and are sealed(lead tags with a cavallino) This car must have been produced when they had an extra challenge engine or a streetcar one not avalible. The difference I heard could be a couple of horsepower, due to the fact that the cams were set and degreed for the Challange series. So, there you have it. Check your timing covers for the seals or at least the drilled out holes where the wire was placed through.