i'm going to refresh one of my total stock 1970 340's

By Molnar crank and roods with light pistons, are you looking at stroking it or just building a stock stroke engine with a light weight rotating assembly? I'm guessing that this is more about more power to make the If keeping it stock appearing with iron heads and maybe a day two intake like an LD340, I would probably go to a 3.58 inch stroke and run some iron heads reworked with smaller stem valves, light porting, and good rockers. But that depends more on what direction you want to go and what expectations you have for it.