so i'm rebuilding my original 1970 340

Nat said
i want to have the lightest rotating assembly possible , forged crank h beam or I beam rods and forged pistons , don't want a speed demon more for highway driving ,maybe a road course once in a while \guess i'm going to go roller cam on this build going to use the hughes rockers and morel lifters . not sure which heads and cam to get
Who makes the lightest crank rods and pistons these days also want the best gas mileage possible , i got around 22 mpg with my last 340 but that was stolen
Open to any and all suggestions

Hang on Nat;
IMO, you need to take a step back and read what you wrote; you have two and a half thought streams going on here, and only one can win, and you are embarking down a very spendy road with very mixed results.
Chose two of;
1) top-end power, or
2) midrange torque, or
3) fuel economy
you can have 1plus 2,
OR 2 plus3,
but you cannot have 3plus1
If you chose 2plus3, then you can throw out all those pricey ideas. You can sneak a lil rpm into street application with just some minor mods.
The rest of your combo is gonna dictate a lot of your build.
You said;
don't want a speed demon
more for highway driving
also want the best gas mileage possible ,
i got around 22 mpg with my last 340

This here is very doable with all factory parts. Consider your current combo, as to transmission and rear gears, and consider whether you need to, or are willing to, or can afford to; change any of it, cuz if they ain't already right for your goals, SOMETHING is gonna have to change.