You wont come near that much hp without heads, besides the stock intake, they are the most restrictive part of the engine. You should go with trickflow/afr/or edelbrock heads, they are light being as they are aluminum. The e7 heads are heavy as hell and dont dissipate heat nearly as well. With H/C/I you are looking at MAX 350 at the wheels, take 15-20% for drivetrain loss and you'll get flywheel estimates. If you get a 200 shot of nos you'd be pushing the block to the max, most people say the block can hold 500-550 hp and anything more than that is a ticking time bomb. I have a 93 gt and its in the process of being upgraded like yours =) there are some great aftermarket parts for stangs/5.0s thats the beauty of the car. You'll be spanking camaros in know time, as it is you should be able to beat early IROCs. If you have any other questions, I'll see if I can help out, check out
http://allfordmustangs.com and
http://www.corral.net