So your crank is full of fuel then.
Head gasket could be fine and the hydraulic pressure from your kicks could be breaking the seal. The difficulty is draining the crank.
Leave things open, maybe warm it but that's difficult to do safely. You 'could' pop the barrel and head back on, plug the carb inlet on the engine then spin the engine with a battery drill, most of the fluid will blow out of the plug hole and the exhaust. Not pretty but effective. Then a heat gun warming the area under the engine where the crank is may help clear more.
One thing is for certain it wont start in a month of sundays at the moment.
It sounds like your actual problem is with the float valve in the carb, it isn't sealing through dirt or being worn. That has allowed the engine to fill with fuel, literally.
You need to look at this, otherwise the problems will keep repeating, with a dud float valve you may flood out in town riding, even hydraulic lock is possible which can crack pistons and heads.