Hi I have a 96 GT 2v with the non PI heads.  I currently had added a vortech s-trim,3.73 gears,MSD coils and wires, 40lb injectors, big mouth mass air,long-tube BBKheaders, shorty X-pipe,flowmasters, and a BBk fuel boost pump. With a custom tune I only made 300 horses. I was wondering if I added a set of comp cams and snow performance methanol injection with out changing the heads would I get at least 400horses?  Will it be safe for a bottom end that has 110,000 miles on it?  

I will assume you're running about 8psi of boost with the stock Vortech setup. You could reach that 400hp mark with more boost and help from water/methanol injection, but i would spend the money on a good short-block first. Then add some ported heads and cams and leave the Vortech as is. That should get you well past where you want to be, safely and reliably.