Scott can get a new set of heads no problem, these days the time frame is always a question. I think people buy them used because they don't wanna spend money for more than something like a -1 head. I have sold probably 7 used sets of B1's myself. As for a Predator head it is far superior to the B1 Original or MC head, easier to put a combo together than a TS and then there is the unicorn PSO stuff. different conversation there IMO.

As for carb size I would be say bigger will make more power. My current B1 deal has a 4150 on it because it was built for NSS stuff. But it has gone 8.90 at 3460, and even as good as the 4250i on it I m confident that it will be quicker with a good dominator. But until we run it and see its speculation.

But lots of ways to get to the power level the OP is looking for. Just personal preference.