Need a plan - component selection for restoring 68 340 that runs on 91 oct

And there is a second witness to what nm9 said, in that the later Low-C engines weren't much, if any slower.
And then there's the math.
But since you say you need pistons, and a cam, really you have almost a clean slate. Now,if you could loosen your grip, just a little, on those X-heads........
But then it wouldn't be a "restoration" any more,lol.
But since you are asking about cams and compression and pistons........ it ain't a restoration anymore either.
So, then which is it?
You could run it as a purely stock restoration, with the addition of water/meth injection for those occasional WOT blasts. Or even just an Octane booster, either in the tank or also injected.

But as far as that goes; Wrymrider has some great ideas; I especially like more cubes,lol, 367 is a fantastic number! And I'd like to try those step-pistons in SOMETHING.
Why more cubes? Cuz you can run at least one size smaller a cam, without losing any street performance with the typical 3.55 gears. And pick up a ton of low-speed performance and even fuel-economy. And in your slightly heavier Heavy-A-vert, that could be, depending on your driving style (like with 4 passengers ALL the time), That could be a real boon. FormulaS Barracudas are NOT light. And the vert will easily put you into or close to B/E body territory. Mine is 3450 with aluminum; heads, intake,4-speed case,and wheels, plus lightweight RX-7 seats and NO rear seat at all; but with; a 23# GVOD added, TTIs and full-length 3" duals, P/S and P/B.
>The fold down rear seat weighed 70 pounds, same as the dual exhaust.
>The GVOD and Passon aluminum case, weighs same as the original 4 speed.
>The aluminum heads and intake allow me to keep the ps/pb for about a zero weight penalty over stock.
>The al. big wheel/fat tire combos, weigh similar to the factory Rallys and skinny E70-14s