the stock manifolds have a 2 1/4" collector on them, correct?

I am having issues finding a 2 1/4" collector to bolt onto them. I can find 2 1/2 and 3 no problem, but not 2 1/4.

 

The hole opening in my driver's side manifold is around 59mm...which is 2.322 inches. So I think you are correct....it's an odd ball size. Just like the jacked up triangle manifold on the dual cat cars. I'll be glad when my mac headers get here so I can go to a mini cat setup and get away from my current setup.