340 or 408?

If you ask the questions you are asking, you don’t need to build a 340.

I don’t mind 4.56 gears. In fact IMO it’s the best street/strip gear. I went to taller tires so I’m using 4.88’s now. I’ll see how that goes next year but I don’t think it’s an issue.

Getting 500 at the crank with 340 inches isn’t hard, but you need a plan. And then you have to live with your plan.

If you’ve never driven with 4.56’s then you should at least drive a car with that gearing before you build something.

If you think 6800-7000 rpm is spinning the guts out of an engine then build a stroker.

Be honest with yourself about who you are. If the above stuff is out of your wheelhouse then build the bigger engine.