It may be the cam (that's suited only to a turbo instillation)
But I for one cannot abbide a car that feels like its got only 200 rwhp before turbo. Not with ITB's and seriusly good workmanship.
I look to the simple things, like the knowledge that with the fish tank over the six nibbling piranahs, CMA felt it made less power.
That's it, a guy's opinion Means Something.
I'd have expected much more, even if the engine is green from its rebuild.
So I'm gonna come out and say it.
Somehwere, you need to find it it inside yourself to consider adding a little more volume to the intake , in terms of inlet hole size (an extra 3" hole by junpering an extra y-piece to the existing tank thingy that covers your 6 throttles. And then, at the back by the booster, make a new glass top that adds volume in the gap between the the rise of the hood at the barke booster end.
A flare out in the front will drop velocity, and help add volume to the intake runners above the throttles. At the hood hinges, there is room to tilt the whole glass upwards, and that will make more volume.
If the box has 5 liters of volume now, with an extra gooseneck at front, and a kick-up of the glass at the back, you'll get 6.3 liters volume. Most of the 4.1 Turbo guys find the 5500 rpm its all over, is true. But in your case, its got huge throttles and really nice porting, so keeping the runner above the thottle volume low ins't a good idea, IMHO.
Have a think on it. I can send you a picture of what I think you should do for modifying it, (George's DIY Turbo Experiement nailed the growth of power up high with simply a huge letter box. You know the one in the fomerly Brandy Wine Cortina, now green.
I appreicate you have gotten your turbo Life back, and maybee baby steps are quite okay. For me, the GM Sat Nav and HVAC display engineer George C got the whole package sorted with simplicity (well, lets be brutal...he screwd over a letter box and made it an iron lung....).
If its got the power potential, don't be scared to go Postal on the Letter Box.....