If you're pulling the drive off of the bellhousing, sometimes the driveshaft will stick in the flywheel coupler. If so, then pull the coil wire off or flip the killswitch to "off", make sure there is no prop on it, leave 2 nuts barely screwed onto the threads, and have a buddy hit the starter while you pull on the drive. The stuck driveshaft will pop right out of the coupler.

mc

Not to bust his bubble but I've had to take a sawzall to the input shaft several times because it wouldn't release from the coupler. I've found that the long blades with the grit for cutting cast iron soil pipe work the best.