Tom Valletta notes that "machinery" can be any type of complicated work (see Noah Webster, American Dictionary of the English Language, 1828, s. v. "Machinery"). [Thomas R. Valletta ed., The Book of Mormon for Latter-day Saint Families, 1999, p. 178]
We Became Rich in Buildings and in Machinery
Brant Gardner writes that if we assume that Kaminaljuyu was the city of Nephi, then during the time period discussed by Jarom we find some interesting correspondences to the account of being "rich in . . . buildings, and in machinery" (Jarom 1:8). Researchers have found in the Middle and Late Preclassic years that,
religious architecture got off to a good start. Temple-pyramids, which in some cases served also as burial mounds were arranged along both sides of a long rectangular plaza or avenue. Religion was the driving motivation, and all nearby peoples must have contributed heavily, in time and muscle, to the necessary labor force. . . . The glory and luxury evident at Kaminaljuyu can only signify a high degree of social stratification with wealth, power, and prestige in the hands of an elite few.
[Brant Gardner, "Book of Mormon Commentary," [http://www.highfiber.com/~nahualli/LDStopics/] Jarom/ Jarom1.htm, p. 10]