I can't feature using a "special jig" which plugs into the pilot bearing hole. I would like to see one of them critters. I use a magnetic base and stick it to crank flange. I prefer a Noga holding system. It is very stable and it is easy to set up and I get the same reading every time. Clamping on to a flywheel bolt with a c clamp or a vice grip would probably be acceptable. However, the only way I have ever seen flywheel housing runout measured is by using a magnetic base on the crank flange.
