Yep, they're on commission! Plus, most of the Auto Zone/Advance/Pep Boys/Etc. counter guys don't know diddly about fixing cars, they only know how to punch a computer keyboard and mis-read the part number!
That "free" manifold might be worth exactly what you paid for it, too! If it's a high-rise, single-plane type, it's only good for high-RPM, full-throttle operation. For street use, a "dual plane" masinfold is what you need, where 2 cylinders from each cylinder bank are supplied by the same side of the carburetor. For instance, the #1 and #7 cylinder, and the #4 and #6 cylinder will feed from one side, and the remaining cylinders will be supplied by the opposite side of the carburetor. If there's one big hole under the carburetor flange, with eight runners coming from it, RUN, don't walk, away from that installation!
Jerry
