I want to build my 2001 mustang gt to 350 HP?

I have a 2001 Mustang GT I want to build up to 350HP my current mods I have on it now are ford racing intake manifold, bbk off road x pipes, msd blaster coil packs, SR cold air intake, short throw shifter, and 4:10 rear end gears which I'm currently switching to 3:55 soon my question is what can I do to get my car to 350 HP because I know stock is about 260

Based on the mods you have installed already, I'm guessing your hp is already around 300 to 325. I'm not sure if you have already done so, but I would suggest getting a tune from Bama performance at americanmuscle.com. They will ask you for a list of all the mods you have and write you a tune that will reprogram your cars computer to unlock the potential of all your mods put together. A Bama tune installed on a stock car will add on at least 15 hp, so with all the mods you already have, you should easily be able to reach your goal of 350. Bama performance will want to know each and every single mod you have so that they can write you the best tune. The tune itself will reprogram several air to fuel and multiple component timing variables to use each and every mod to its full capacity.
On the other hand, if you already have a tune that has been written to contain all your current mods, then I'm afraid you have pretty much maxed your cadr in terms of hp, unless you go supercharger.

A set of cams and pair of aftermarket heads will get you 350 HP. Keep in mind, in doing so, you'll be giving up a bit of low end grunt as well. If you're staying N/A keep the 4.10 gears.

Like most factory engines, the big bottle-neck to air flow is the factory cylinder heads. You already have the factory PI ( Power Improved ) heads, so next up is a set of aftermarket aluminum heads. Look at a set of Trick Flow for your single cam engine, with a better cam.

With what you have now, get a nice set of cams and some new heads and you'll probably be a little over 350HP. If you're not, get all that, and a tune, and you'll hit 350 or more for sure. You're real close man.