When you turn the motor over be sure to watch the rear piston when it is going down. It could lodge in the spigot, hole on the engine case. You can use a 2x4 to tap on the stuck cylinder to try and get it to move. Keep us posted.
tourbox
If you have not already dump some kerosene down the cylinder and let it soak, if i remember right older sporsters had a drain plug on the bottom of the case