First time Holley tuning help

Forget the vacuum advance until you sort out these issues. Adds another fly in the ointment.

You could wire the secondaries so they don't open at all. Then go hammer it. See if it still bogs. That's quicker than changing springs. If it doesn't, put a stiffer spring in it.

The rear metering plate, 134-9, that comes factory on those carbs is equivalent to a 64 jet. You got a BUNCH more rear jet in it at a 70.

Those universal 600 vacuum carbs are usually pretty solid out of the box.