I'm saying two things:
1) The power band will be at pretty high RPMs, this is because the flow capacity of the carb, the ports and the valves is quite large so at lower RPMs the velocity in the induction system will be low such that the late closing intake valve of this cam will blow much of the mixture out of the cylinder as the piston rises until it gets enough RPMs to where the incoming mixture velocity can overcome the reverse pumping forces of the piston. This pushes the torque peak toward the RPMs of the horsepower peak and softens lower RPM power. Also an associated problem with this if you're running an automatic is the need for a higher stall converter. This works like a slipper clutch allowing the engine to rev up into its power band before loading it.
2) You have a lot of good parts, but some of the selections like the 200cc ports and big valves are overkill on a 350 that doesn' turn 7000 RPM. They can be tamed but it takes a lot of time and testing to get there.
There is a point where it's hard to tell if the engine's power issues are the result of tuning or of large capacity components working too far from their best solutions in terms of displacement and RPM. There is a lot of work after putting the parts on an engine, the further the part selection gets toward high performance the more the work is involved in getting them settled down.
You've hit into one of the reasons the Vortec head is so popular for hot street and certainly off road 350s, because they offer a significant power boost without resorting to large cams, big ports and valves. So they are much happier when mated to an engine that runs from idle to 6000 or so RPM. Your big port and valve choice of heads will take some extra work to get them working their best.
I would ask if you know the static and the dynamic compression ratios of this engine. The both compression ratios against the cam timing is very important to getting all the power you paid for, again because of the big ports, valves and cam timing the compression is used to restore power lost to the reverse pumping effects. So knowing the deck height, thickness of the head gasket, and the volume of the piston's dish is important to computing the compression ratio. For the dynamic CR you need the point where the intake valve closes as well and the rod length. you can play with the numbers at this URL.
http://www.kb-silvolite.com/calc.php
So I don;t know if this is a tuning issue or whether the power band is just higher than you realize. But first you need to understand what you've got for compression ratios, that will lead into what the timing needs to be both in terms of how much but also when it comes in. You need to figure out the mixture ratios, it's unlikely the Holley is correct out of the box.
Bogie