I've looked and looked for a manifold with the bigger outlet. I have either six or seven now. all of them are 2" or less. I would love to find a big out manifold before I put this back together. I don't see it happenin.
The industrial application of the Slant 6 on the John Deere Swather had the big maniflolds. Talked to the guy about it when I sold him the replacement slant 6. Unfortunately his big manifold was cracked, so he just used the truck manifold on his application.