I had worked at GM for the last 7 years, and part of my job was setting up the final bore and final production hones as well as write the specs for them and monitor capability. I can tell you the crank bore tolerences were no worse than +/- 0.012mm, with most our lines running around +/-0.008mm and run-out was only allowed 0.025mm from front bore to the rear bore max.

Cylinder bores were only allowed +/-0.011mm and a max of +/-0.008 on the thrust wall and cylindricity of 0.013mm max and max taper of 0.007mm. And just in case you don't think it can be held, it can be, and it can be done day after day, week after week, etc. The machines use in-line feed back to constantly hold size.

Years ago, the sizes and tolerences were not this tight, but to meet the ever increasing demand for 100k warrenties, and not go broke in the process (on second thought, I guess they did go broke), all the specs were tightened over the years. If your measuring in thousandths, your already oversize....