Kansas Kustoms has a good reputation for splitting manifold and the person that now does it was trained by Kansas Kustoms. That person (don't remember his name) has posted recently on Inliners, but right now Inliners web site is having some problems, so I can't get any more info for you. I have a set of long tube headers and they have been a PITA to get to seal up. I've also heard that you can only split the stock GM manifold 3-3. Considering that you can only split 3-3 and that even the best on occasion have problems with their welds on cast iron, I'd look at Langdons cast headers.
Larry
