I was surprised to see the >900 hp number too.
But everybody should remember, the heads had some work, not OTTB CNC345, and the -3X intake was tweaked. And he does have a vacuum pump on it.
Still, better numbers than I expected. If, if, if, we ignore the drop at 6800, and peak at 6900 rpm, this dyno still says 910 ish.
About the most I could expect from a 540 CID with CNC345 heads.