With the engine front cover off (remove neg batt lead first), the 6 mm bar stock fits into the alternator bolt (which is crank mounted) and then I bolt the cover back on. You want to ensure the overall "tool" length is such that the cover is jammed against it, thusly holding the crank from coming forward. My cover has about a 1/4 inch gap when it's snugged up with the tool in place.
Have heard of the rag stuffing....I'd be afraid things still might move. I got to see these mystical thrust bearings and the pins they hang on inside a cutaway engine at Super Tech. You really don't want that puppy popping off. The crank has to be restrained from moving forward even 1/4 inch.