Ok I am planning on building a firebird performance project in the future. Here are my plans Blueprint Engines 383CT Claimer 426hp/433tq at the flywheel t56 transmission 3.73 posi rear 10-12 inch wide tires/rims in the rear 9 inch in the front its going to be lowered 1 inch, by cutting some moog springs, I will be puting LCA relocation brackets, adjustable pandhard ber, some better sway bars, I am making the car for corners. I am going to try to get it down to 2800-3000 pounds. Any idea what this would run in the 1/4 mile?

If you actually make the claimed HP of 426 and get to a vehicle weight of 3000lbs with driver - It will be capable of running 11.18 @ 121 mph assuming the car is effecient. However that flywheel number is probably sea level corrected, and the car will not be effecient with your cornering plans, and that would also assume you could pull off a 1.50 60ft with the t56 and 3.73 gears - all doubtful.. With that being said Look for bottom 12s - 12.0 range.
But with the weight and HP it is capable of trapping 120ish in good air. If your not close to that, your either not making the power or driving horrible, or weight is no where near 3000 w/driver or all of the above.
That number (3000lbs) will be hard to get also with big wide rims, Heavy suspension upgrades, wide tires, sub and strut tower braces ect.

Also, any suggestions for an improvement in the setup would be appreciated. I need to figure out exactly what I want before I even start. I dont want to be buying parts that will end up limiting me in the future.

Also, the weight reduction Im not to worried about. I am plannign on removing almost everything. Back seats, carpeting all the interior trim. Basically all I will have is a custom dash on the drivers side with gauges and two front seats.