I'd look a this next. The idle can 'hunt' when the PCV close-down level is too close to idle vacuum.
Measure the idle vacuum cold and then as it warms up and see what you have. It could easily be a PCV valve that is open to cruise opening at cold idle and then closing down to idle flow level as the vacuum comes up a bit with warming up, and thus effecting idle in the carb, with the carb being set wrong at cold idle to compensate for the cruise PCV flow it is seeing then. It may not be the only issue, but that needs to be checked.
What PCV do you have, OP? (Assuming you have one....)
