435 horsepower in 1955.....

[Fordors]

Boost, especially high numbers, will not necessarily equate to better performance. A GMC blower is really just that, a blower, and as such will only make "boost" as it packs the intake tract from the valves to the intake manifold. Picture a plastic bag laying on the table, it is at atmospheric pressure. Now take the bag and blow it up, we have artificially "boosted" it's internal pressure.
Depending on the cam timing and how efficiently the complete intake tract of any engine is designed/refined will have an effect on HP. Spinning the blower faster will make more boost but not necessarily more power. Many other factors will come into play; is the cam optimized for the intended purpose, is the static compression sufficient to really utilize the boost with that particular camshaft? Barney Navarro was a thinker and as such I'd bet this whole package was very well planned. It's the total combination, not just boost, that makes the best performance.