It sounds like you are describing the outer plug, I'm talking about the inner one. Maybe I worded it wrong though, just going by the parts diagram.
It is quite possible the previous owner epoxied the plug in there it should have been easy to pull the plug. Unless you were turning it the wrong way
It is just a plug with a washer, maybe you can take it to a local machine shop and have them helicoil the threads for you. just take them the float bowl
I`m sorry I thought all flywheels had the 1/4 20 puller bolt holes I never pulled one of those flywheels. The technique is the same tho.