What kind of EGTs did you see on the dyno? Stock pistons don't seem to like a lot of heat, but you're shoving a lot of air so the pistons might be relatively happy.
H&S squeezed over 1000 out of the Duramax stock bottom end. Surely a 6.4, that is known for a it's strong bottom end, will hold up to more, at least for a while... 2000+ ft-lbs is still a lot though! :hammer: