Which one? 2- or 4-barrel? What compression? Which pistons are in it? Ever been rebuilt? If so, it's not "stock" any more.
Which one? Square-flange or spreadbore? Vacuum or mech secondaries? What CFM? 4150 style, 4000 series, or Dominator?
Which ones? (casting numbers ONLY, please) What chamber cc's? What work has been done to them, if any?
"Stock" isn't much of an an answer, unless it goes along with the exact specific description of what it's "stock" for. There's an INCREDIBLE variety of "stock" 350s.
What cam is in it?
What tuning has been done to it? Have you carefully tuned the carb and the timing curve for best results? You can take the same "parts list", and get it to either beat the OE gas mileage specs (if there were any.... I don't recall there being any invented yet in 71) or to drink it like a broken hose, depending on the degree of tune.
Help us out, and maybe we can help you out.