Well I have to say that I got very lucky. I had a tech come over Friday night to look at this and another issue which I believed to be related to the fuel lift pump.
First, he found that someone had installed an electric pump inline, right before the mechanical lift pump. He said this was commonly done when the mechanical pump gets weak or fails. Apparently this pump was DOA and somewhat of a mystery how the generator was able to run at all. New electric pump has fixed the issue. (I also have a spare mechanical pump, but we didn't bother installing it.
Second, and here's where I got very luck. The smoke was apparently from the voltage regulator. Despite no visible burn marks, the potting material was severely cracked in many places, so it would seem the components imbedded my have cooked and caused the smoke. He tested the exciter, stator, etc for proper ohms and all looked good. Fortunately, I had just ordered another SX460 AVR which is the same one I used to repair my M643 a few weeks earlier. The SX460 is not installed and the generator is running perfectly once again.
Just wanted to update the group in case anyone ever has similar issues. BE SURE to look for an electric pump. In my case it looked more like a fuel shutoff solenoid so I didn't think that was the issue.