e-bay #271358759025 & #321205384274 are both the better manifold--the clue is the 2-1/2" dia outlet and the outlet being more or less positioned beneath cylinders #4&5-also in other views the runners run farther from the head before they join the "log portion" (more streamlined) compared to the other 194/250 chevy exhaust manifolds which have a smaller outlet and it is more centered along its length--much more "jammed up" passages tight to the head.
