These guys are making in excess of 1230hp +- with N/A 565cid and conv. heads (if thats what you choose to call them) and according to Chris Uratchko, he says that they made 1230 almost everywhere on the dyno sheet. Better have a thick wallet though$$$. Pretty good thread on the Bullet about this.
Texas pro stock heads - Yellow Bullet Forums
If you check out post #88, they are working with Brodix to produce a head, it will require custom pistons, rocker system , changed valve angles, and they still call them conventional,lol.
Pics of them in post 104