I believe the Dvorak ironworkers were originally built in South Dakota. Joe Dvorak was a machine shop owner, who, many years ago, came out with one of the first hydraulic ironworkers.
North Dakota may be a "heavy industry desert" as you say. However, in South Dakota, there was K.O. Lee at Aberdeen, SD- manufacturing a line of precision grinding machines. Also in Aberdeen (if I am not mistaken), was the Hub City Ironworks. This was a firm based around an iron foundry which produced a lot of gear reducers and driveline parts for the agricultural and construction machinery industry. The castings for your shaper may well have been jobbed to a foundry in some place other than where the Dvorak shop was that built (and put their name) on the shaper.
Prior to 1976 and the Clean Air Act, a lot of smaller iron foundries were in operation in the USA. These relied on coke-fired cupola furnaces to melt the iron. A combination of a move towards welded fabrication to make parts (aka "weldments") and the clean air act spelled the end of a great many of the iron foundries in the USA. Up into the '60's, a lot of towns had some localized heavy manufacturing and often had an iron foundry or drop forge shop. While North Dakota may appear to be a "heavy industry desert", and may well have always been one, Dvorak and the foundry that poured the castings may have been down in South Dakota or some other of the North Central States.