Crank pilot concentricity
I would use a steady rest on the number 4 main bearing and indicate it in on the 5 main and then check the converter pilot bore.
Of course, if you don’t have a steady rest that would make it more difficult.
EDIT: you can also put the steady rest on the number 5 main bearing and indicate it in on the flywheel register right there on the back of the crank and then just drop the indicator down a bit and take your measurement.
Or you can put it back in the block as mentioned below.