Yeah that's the case sometimes. It just doesnt come off as it being the exhaust system that is responsibleas to why this thing isn't making more then mid 400's. Even seeing "triys"...lol..love the way some type, and that cam, speaking of which was ground with those in mind I'm thinking.
You hit it imo and I just caught it like the Tri Y thing, "2.14/1.81" .....wonder how much was blended, or not.
Bigger valves need bowl work flow well and or at least a good throat cut to not go the other direction ...that can be a killer.