Wow, that was a pretty substantial gain.
My coworker did this to his Ford f-250 Turbo Diesel. He has around 850ftlb or torque at the moment.
The main thing he learned though, change out the head bolts/studs. He ended up floating the heads and blowing the head gaskets due to the extra boost at WOT. Hasn't had a problem since he moved to ARP.