[Fasterthanyou]

He needs headers plain and simple. The weight reduction is a no brainer when you're power limited but to ignore a bolt-on like headers is just beyond my scope of logical comprehension. DO IT, just do it, do it... in my best Maury Finkle (from Starsky & Hutch) impression. If you get me a stock manifold to model then get a couple flanges made up, order some piping with bends and for under $300 have some custom made headers and y-pipe. I think wasting time on just a y-pipe isn't going to help much. Not compared to doing the whole thing in one sitting. I've made custom headers in very tight places that were equal length and side exit... your setup would be a SINCH to do. Especially with all that room you've got to work in. Even if you had to take a piece of flat stock and drill/grind away a flange it wouldn't take nearly as long as you think. Just get some gaskets from GM to get the pattern and some stock, trace, drill, cut, and grind .
I know I'm pushing this hardcore but I think what you're doing is awesome. I just want to see it as fast as it can be and headers are SO important even on an relavitely new engine like yours.