From your description, you're probably headed to the machine shop anyway, even if you get it lossened up. One important thing would be to make sure there is nothing else locked up, making it appear it's the motor, (broken trans, clutch, etc.). I have, on occasion, loosened a stuck piston by liberally using light penetrating oil in the cylinder, then putting the bike in 1st gear and rocking it back and forth, bumping the motor. This way you're trying to move it in both directions. Using the kick starter isn't always the most effective. Best of luck, and enjoy it when you're done!
...KP