Wow, this is taxing the old brain to dredge up stuff from years ago.
We never dyno'd my car with the Thagard manifold, but did a pretty scientific study with datalogs. Specifically, I datalogged rpm, MAP, and wideband AFR on the original ported N42 manifold with a 60mm throttle body as a baseline. I then installed Jame's manifold with the same throttle body and injectors, and made sure that the boost setting was the same. We used a good closed loop HKS boost controller which needed no readjustment, and pulled another datalog. With all other conditions the same, We recorded something like .6 AFR leaner in the higher rpm areas( more than 4500 or so up to redline as I recall)under boost. Interestingly, AFRs were actually a little richer than the stocker mani in the lower RPM cells under boost. We were testing at about 17 psi, at about the 400whp level.
James postulated that,when we tuned for the additional airflow, we would gain somewhere in the neighborhood of 35-40 hp. He actually posted some graphs on his old website as I recall. I don't remember if the power gain could be felt by the butt -in fact the boost at higher RPM at some expense of spoolup mitigated the enhanced power - but definitely could be measured. We never backed up these experiments with dyno numbers or comparative dragstrip times.