After looking a little closer at the ebay piece, I can see where it might not be optimal with the cross flow. The Mr. Gas is just a merge point between and flow does not actually intersect.
Of course if it was me, I would get a couple of mandrel bent els and build my own Mr. Gas lookalike for $40. There really is nothing that special about the design from what I saw. But, then again I do all my own exhaust with mandrel bends after I found out I could spend a little time and have full mandrel exhaust. Most people dont want to mess with it.