I agree with you about the Pontiac exhaust manifolds, especially the aluminum ones! They even paired up the correct cylinders in the correct Tri-Y arrangement: 1-5, 3-7, 2-4, 6-8. Exhaust scavenging has always been an interesting subject to me. Chevrolet at least halfway tried this with the #925-926 HP manifolds. If you look closely at a set you'll see that on the passenger side they paired together 2&4 and then 6&8 which is the proper way to do it, but on the driver side, it's a little harder so they just compromised by separating #7 from 1,3,5 which all three dumped together. This was a vast improvement over the 1961-62 manifold which are jut lumps of cast connecting the exhaust ports together, There was a musclecar magazine that within the last couple of years did a 409 Dyno test and even compared the '62 to the better '63 manifolds and showed the results which I can't remember the increase at the moment.