Well,
There are two schools of thought on the heads.
The fisrt is that a bigger head will make more power, period. But, (there is always a but) more peak power at the cost of some torque.
The second is that a smaller cross sectional area like, ovals or small square ports will have a higher port velocity and make more torque without sacrificing as much horse power on the big end.
The wrench in the works, my brother bought some 18 degree heads for a small block, they flow as much as most big block heads. Dart claims as much as 150 more or more horse power, and they reccomend going as big as possible.
As for your combo, why only 11 to 1? Both of those cams look like they needed a little bigger compression.
The nitrous will help. Check out nano nitrous, if you're going to run nitrous. In one season it should pay for itself.
All the dominators I ran had a really soft bottom end so that will help with launching. If it feels doggy or squish-y on take of try a 750 or 800 carb with an adapter. It should only take a few minutes to swap at test n tune. You could swap the spacer out for an adapter.
Why are you running the 4.56 gear with this combo? Already had it?
Does you TH400 have a transbrake?
What are you looking at shifting it at? 7000 or 7500?
Here is a site with some drag calculators: http://www.wallaceracing.com/Calculators.htm
If you got HP number you can tell pretty close to what it will run.