Does anybody remember mobile engine overhaul outfits?

One of my early memories was in about 1951, when the 1947 Buick straight 8 that belonged to the man next door wouldn't start due to low compression. So he called out a mobile engine overhaul guy who arrived in a big truck that had machine tools inside. I watched him work on the Buick all day, and was fascinated by the way he bored the cylinders, ground the valves, replaced the pistons and ground the crankshaft rod throws while the block remained in the engine bay. In fact, I think it was this experience that first got me interested in working on cars.

Does anybody remember these mobile engine overhaul companies and how they worked? If so, please relate your memories. Thanks.