Well, a port and polish of the intake w/ port matching is worth quite a bit for the stock vortec intakes. It will flow much better. You will have no need for an aftermarket intake (especially since one doesn't exist). Your HP gains are optimistic. Custom tunes get rid of/adjust rev limiters and top speed points.
You may see 400 hp....all those mods will equal a cumulative power increase and each individual "claimed" HP increase are really just generalizations based off a stock motor vs. a stock motor w/ that particular mod. You may see 400 hp at the fly....MAYBE....
On the banks exhaust, do you plan on getting the headers or only the cat back?
The nitrous will be better plumbed into the intake tube.....It will atomize better there...I would not do it on a TB plate....
Do you have a limited slip or posi rear end? Are you planning on a torque converter? Probably be a great idea if you plan on hitting the strip...probably a 1500-1800 stall. Do you have a shiftkit and or vette servo? The transgo shift kit and a vette servo will be a very very good idea for the increased power. You will also want a secondary transmission cooler.
Whos' doing your custom tune? Westers? SPE? Ed Wright?
$2500 a piece for LT1 heads?!?!....explain? That is $5k for heads....hope they are made of gold.
Something to think about...pullies underdrive accesories and you'll be pulling more amps with a dual fan electric kit. May have some voltage issues...
If your gonna juice an engine you may wanna consider a cam...something a little more juice friendly.
My brother just bought a 97 vortec 355 with these mods:
1997 Vortec 350, .030 overbore (355 ci)
Polished Crank
Speed Pro Forged Pistons and Connecting Rods
Completely Balanced Rotating Assembly
Stock Vortec Heads Rebuilt w/ Mild Port & Polish
Milled for Heavy Duty Valvesprings
Comp Cams Compucam - 212/218 488/495 112* lsa
Miloden Oil Pump
Cloyes Double Roller Timing Chain
Stock Intake w/ Stock Fuel Injection
Intake Elbow w/ Computer Matched Granatelli MAF
Stock Ignition Components
Helix TB Spacer
SPE Custom Tuned PCM
That is a solid 300 flywheel horse motor w/o nos. W/ a 150 shot it may see around 430....
There isn't any way you'll see what you think you'll see w/o a cam, complete porting, port matching, and polishing along with some other considerations.
Cameron