I would not use the piston stop on a big block. The angle is too shallow and close to dwell point.

Love the flat bar idea, 2 or 3 holes will absolutely hold things still. Especially in a shear. I'd aim for bolts 1 and 3 or 1, 2 and 3, 4 or 1 and 3. Just not 2 beside each other.

Or the flywheel teeth. I mean not blindly jambing something in there but a chunk of soft metal like aluminum will not hurt any teeth. I've done this many times with a large screwdriver or prybar. Just understand how to get it stuck so the load is square to a tooth.