Even with a bad petcock, the floats should keep the gas from free flowing unless there was just a really slow seep over time, so I would look to the floats too.
As for "rebuilding" the carbs. Some float bowl gaskets (or gasket paper and some scissors and a hole punch, like I did) should be all you need. These carbs need to be clean...cleaner than clean, to run correctly, but there should not be much of a need to go changing parts. Jets (and everything else) can be cleaned, so I would do that rather than replacing anything. Only replace parts that are broken or bent. I am running 100% original '79 carbs and they work flawlessly- jus needed a good cleaning. Save your money for other things.
If the oil has no gas and no more gets in it, you should be good to go for the next 1500-2000 miles, and keep that interval in mind- no 3000 to 5000 intervals like cars. Meshing gears and air cooling is harder on oil than what your car is.
Test the petcock. If it is original, it should let no gas through if the engine is off while turned "on"- but gas should flow freely on "Pri" (prime). If it does that, no problem. If the gas flows with the engine off anywhere but "Pri", a rebuild is in order, but I would cut out the hassle and just install a manual petcock, but that's me.
