Gas Mileage???

Oh chit, Brasil did you say 340?
I screwed up and nobody caught it.
But the good news is I screwed up twice and they cancelled each other out.
So reworking the formulas for a 3.31 stroke and one size smaller cam to get the 15 inches idle at 16* timing , all the numbers work out close to the same.

And so, back in 99 I ran my aluminum headed 360 at 11.3 Scr with a 292/509 on 87E10 with no detonation at 34degrees. The Wallace calculator says the Dcr on that was 9.03/186psi.
Your 340 with say 11.2 and a 270/110cam would be at 9.1/188. That's about the same so it should be easy with your cam, and should be dynomite with those 3.23s. You are gonna need more rubber tho. It will certainly be infinitely better than it is now. And you will finally be able to run a Vcan.
So off with a head!