I am certainly no expert but I would not get too worked up over the dyno numbers. Would be good to know what kind of numbers have been recorded on that specific dyno for comparision purposes. There can be huge discrepancies between dynos.

However I would also be surprised if this combination make power gains above 5900 RPM. I have not looked at a set of stealth heads myself but the power might still be head limited even with max porting since the cross sectional area of the port can become the limiting factor for the cubic inches that you are trying to feed.