If I was not using an impact wrench to remove the bolt I would either engage the clutch with the pto switch and then put a strap wrench on the pulley to hold it or I think that on the flywheel side of the engine you can use a small prybar or large screwdriver to hold the engine from turning at that end. You will have to remove the access panel on the RH side of the dash tower to accomplish this.
The hydraulic pump end of the vanguard engines have a stub shaft that sticks out which has some flats on it. You can get a large wrench on the flats. No idea what size wrench. I've used a large adjustable wrench. Another option is harbor freight sells a $40 electric impact gun that's actually decent for the money. The bolt comes right out using it.
Last edited by Matt A; 10-29-2020 at 10:03 PM.
Reason: Changed the word PTO to Pump as I had intended to type before.
Taking it off, is the easy part. Putting it back on at the correct torque, is the tricky one.
Someone shared a tip and it worked perfectly for me.
Pull a spark plug, rotate the engine by the PTO mounting bolt, while feeling with a dowel until the piston is fully retracted. Then feed as much clean nylon rope into the cylinder as it will take. Then start tightening again. It'll eventually tighten solidly and you can get a decent torque reading. You'll then be able to reverse rotation just a bit and the rope will come right out with no harm done.