422 dyno fail

How accurate are the OEM parts he’s using, how about the timing marks on the damper? Port work can cost hp as fast as make it. I ran a name brand manifold from the 80s on the dyno because I had suspected it lost power back in the day and it did, 85hp less than an M1 single plane, this was on on of my 440s, took twenty minutes to change the manifold.
I think it’s like stack tolerance where you get enough things that are just enough off so things don’t fit except here the stack tolerance comes up with with a motor that doesn’t perform as expected.