I grew up in Braham Mn, live about 15 mi. from there now. The Dalhman corp is still in business but doesn't make potato equipment anymore. They put rubber coatings on things like the chain parts for potato diggers and such. They quit building diggers and planters in the mid 70's I think. Originally they were an oliver green color, then green and white and in the end I think they had gone to blue and white.
I remember as a little boy they came to our farm on a number of occasions to take measurements off our 830 case so they could make a mounted digger for them. They also came to our farm to test a rock picker they were developing, but as far as I know none of those were ever sold. I remember that it really did a job of getting the rocks tho.