so i'm rebuilding my original 1970 340

Well...this is obviously a 'drooling over the parts catalog' type of question, because the OP doesn't really know what he's asking for, or why.

But fine. Everyone has missed the mark entirely. Scat? Puh-leeze.

Call up Crower or Winberg or one of the other top shelf crankshaft guys and order a 3.31 stroke crank made to your specs....tell them you want it as light as possible. They will make you any stroke you like, none of this 'can't get it BS'. Then, get some SB Chevy titanium con rods. Then, call JE or Diamond or just about any top shelf maker and order a set of pistons with pins....tell them you want them as light as possible, regardless of strength.

Make sure you tell each maker that cost is no object - that will be important. But it's clear that nothing less than the ultimate will do and by God, you shall have it.