Take a inner sheave from a torque converter, or probably the outer case of a centrifugal clutch or anything round that is 3/4" in diameter with a key way in it and drill two holes in it that line up with the holes into which you would bolt the torque converter mounting plate on the PTO side of the engine.
Bolt it snug and it works great for breaking the flywheel nut loose as well as for torqueing it down when installing. I was quite surprised nobody mentioned this. It is a very positive and safe way to lock the motor up. Saw this on a video some time ago, thought everyone knew about it.
I never bothered with anything like that becuase I would need 2 maybe even three for each size PTO, Then it rules out servicing say a vertical engine, genorator, small outboard, etc.. or lets say you just wanna pull the flywheel on an assembled bike, you know the ones you always see that "just need points, and a carb adjustment" listed for sale. Then there are the older Tecumseh/lauson engines I have rebuilt where they don't have threaded holes in the sidecover, Then I would need something else for a lot of the old Briggs and Scrapheaps etc.. etc... Plus I bought like 7 OEM Tecumseh strapwrenches out of old stock one time for like 12 bucks a piece
Just this month 2 of the engines that were assembled (and painted yesterday) The 1969 Rupp engine on the left is 5/8 and the 1968 on the right is 3/4" output, so that woud have ben 2 tools and take 3 times as long to set it all up, the wrench is just sitting right there already looped and ready to go...........If I ever lose a hand or arm My opinion may change though