Back in my very young years, around 1977-1979, I used to work with a company in Dallas that had large Cincinnati planer. The man that ran that planer was already retired and still working. He started running planers in Saint Louis back in the 1940's. Planed a many lathe beds and other equipment for machine builders back in that time. This guy was so good, he could match plane bed sections on long bed machine tools like the trepanners I used to work on, that would have two, three, four or more bed sections! And when he was done, they would take and bolt the sections together and sight them with a transit and get then running within a couple of thousandths in 100 feet! Tell me that ant darn good.
Getting back to the OP's post above. Those guys back then, I guess they were millwrights that did the scraping fitting of machine tool components together? Anyways, between them and the guys that ran the planers, that planer operator could get the way profile so close, and I mean splitting hairs, that the millwrights had very little scraping to do to make that stuff fit perfectly. If you have the Connely book, look at the pictures of the planers being built and checked for alignment, impressive to me!