Well, since it's stripped. Just remove the rear PTO spark plug, spin the pto by hand CCW until you reach top dead center on the piston. The rotate CW maybe an 1/8 of a turn. Lower some clothesline down into the cylinder, probably about 5' worth, then rotate the pto CCW again until it binds up, then use a pipe wrench to twist the PTO off the crank. Install will be the opposite, but I would get a solas brand impeller tool for a 140mm impeller (about $14 shipped on ebay) and then install the new one and torque it with that.
Before you pull the pump, you need to disconnect the c clip on the driveshaft (See video below)
Pull back on #8 it will expose the o-ring or C-clip if it has been upgraded. Pop the clip or o ring off.. Then remove the pump, steering cable and reverse bucket etc.... Pull pump, remove driveshaft, remove PTO. Probably 1 to 1.5 hours work (or much less if you had done it before) to get the job removed .