If you want to be a beast and your going to build it. With stock sleeves.... The best combo would be an A6 or y7 bottom end with a z6/y8 head. The y7/a6 have been proven to have best sleeves. Also there's a couple of people that have made 250 on that motor with no Vtec (Scotty from Mainstream has my old t25bb setup, and I believe he makes 256on a y7). I made 230 with an A6 bottom end and z6 head at 9psi on a 50 trim. Just headstuds. So 300 will be easy if you build it right. I have done quite a few d series builds. And have great success and awesome failure lol. But you live and learn. Good luck on the build