Add one more thing to look for - engine off - remove the metering rods caps (don't drop the screws in the engine) - start it up and see if the metering rods are bouncing up and down or are they sucked down and stay there or are they up and stay there. If they are bouncing around - hold them down and see if the idle smoothed out. If they stay up - push them down gently until they seat and see if the idle smoothed out while warm. Your comment about surging after warmed up - sounds like they rods are bouncing up and down. The other thing to do is watch the timing when this surging is happening - if vacuum advance equipped - could be contributing to this - and if you have one light and one missing centrifugal advance spring that could as well.