Whats the best way to get this fitting off

SOAK the threads in a high quality penetrating oil for several days FIRST ( I like SeaFoam Deep Creep). The key is DON'T rush it. Soak it several times a day for several days. Then, pick your poison. I would try the pipe wrench after letting it soak. For several days. You'll know if it's going to come out or deform if you're very careful and slow. You'll feel it try to break lose, or you'll feel the fitting try to deform. Watch it where it goes into the intake VERY closely as you try to back it out and you'll see it if it tries to turn or tries to fold in. If it tries to fold in, then is the time to make a slit in it like Steve said and go ahead and fold it in on itself. I try to leave that as a last resort on aluminum intakes, because they are pretty fragile. But go at it SLOWLY and carefully. You'll get it.