Stock jetting is usually a little rich on the top end and a little lean in the low/mids. Gutting the cat shouldn't screw up the mapping as far as top end hp. He should actually see a small gain in top end hp. It's kind of like installing a better flowing can on any other bike. You will get a small gain and you don't have to remap with a PC3 but you might get a little more gain with a very mild midrange remap. There is no chance of hurting anything by gutting the cat.
I am curious to hear if the midrange and light/cruise throttle feels lean at all....... any light surging? I doubt just gutting the cat would cause this but gutting the cat AND install aftermarket cans together might lean out the mids enough to feel it.
Thanks for the pics, those are great! Without having to search through additional posts, can you tell us if you're still running the stock cans?
In looking at your pics, it appears that the cat was only about 1 1/2" thick. Is that correct?