The PTO is threaded on to the crank. SO... since your splines are torn out... you will have to use a big a$$ pipe wrench. You will also need to hold the engine. I like to put rope down into the spark plug hole, to hold the PTO piston. Don't do it in the MAG piston, as you may twist the driveshaft.
It's not going to be easy... so you need a BIG wrench, and you may need an extension to break it loose.