Does anyone have any experience with this Y-pipe? http://www.summitracing.com/parts/EDL-65930/
It's got a 2 bolt flange, which should (?) bolt up to stock manifolds until headers are bought later on, then can be lopped off and re-plumbed with reducers. also had a very "flowing" look to the way it's built.
And let's not argue the thermodynamics of the 2.5" inlet to the 3" outlet...

 

That Y pipe is for Edelbrock headers, it shouldn't bolt up to the stock manifolds or any other brand of headers. Also that junction where the two pipes come together in the Y is a restriction, one of the reasons Edelbrock headers aren't the best for performance.