its been my impression that a lot of what was going on in the early seventies had to do with passing emission standards than making engines run better.

They would have tuned to maximum fuel economy too.

Another component seems to be a high energy spark, John Parker seems to be currently thinking that it can help off-idle throttle response. Seems to eliminate lean stumble without having to adjust the carb so much that you get too rich of an air/fuel mixture at cruise.

With a high energy ignition you might get a couple of extra MPG with a vacuum advance, but you also have to provide a weaker part throttle mixture. What sort of induction have you got?

If you have a stock engine with stock carbs & you also have off-idle stumble, then you need to fix this first before doing anything else.