I wouldnt doubt more than that depending on what your putting in your engine. My tuner estimates 700hp with what I got. Thats before water meth haha. I did all my own fab work, just need an exhaust shop to put in a 3" to dual 2.5" adapter. Thing is way too loud the way it is right now. And when the bov pops it shoots a nice water meth mist haha. Sorry I keep rambling just took it for the first drive today. Dyno tomorrow 
What size turbo you putting on? What water meth kit?
Back Alley Motorsports 98 GMC
-5.3l LM7 bored to 5.7l Thompson Motorsports -72mm T4 Magnum Turbo
-TU1 Custom Grind cam(spec speed.inc) -799 heads
-.660" Trick Flow dual valve springs -Forged Probe Pistons 3.902" flat top