Thanks for the reply. I decided over the weekend to fork over the bucks and buy a new set that is specific to this M400 chassis. I'm also replacing the pipes and switching out the old single muffler to a set of high flow duals. If I pick up 2 mpg out of this, (fat chance) it will pay for itself in no time at today's gas prices. I plan to overhaul the old 440 this winter and have some bowl work done to the heads while they're at the machine shop. I'll install a new rv grind cam while I'm at it. A little extra pep will help me big time, since I like to haul one of my antique tractors to the tractor shows behind my rv.