Just thinking of those roast potatoes that you are about to start - I went out and took shots of what was a very, very common type of potato digger in my youth. We actually called them Potato Spinners because they quite literally spun them out of the ground.
Many manufacturers made them and one of the foremost was Blackstone whose machinery products were for a long period of time marketed exclusively by Massey-Harris for them. We had one at home just like this and as a very young lad I can remember being sat on the MH 12-20 after it had been set in the row and told to steer it to the other end of the field -- we would commonly have about thirty pickers - school kids on half term holidays in October.
Times moved on, my Dad bought a new Ferguson TE 20 and this took over the annual role of pulling the spinner. I remember one quite wet autumn when on exiting the row at the end of the field I didn't quite turn sharp enough and I dropped one wheel of the tractor over the ditch edge. STUCK. My Dad came calmly up and asked "field not big enough?" What a flattener!!!
Now Malcolm and I have never seen this type of potato digger in N America. Did you have them over there?
Before the days of tractors they would be drawn by a couple of horses. The great thing about them was that you could dig potatoes in quite wet conditions which woud not be possible with today's enormous harvesters. They were quite simple - the share ran under the row of potatoes loosening them, then the primary spinner spun the soil, potatoes and haulm out to one side and the seconday kicker caught the haulm and spun that further out of the way to leave the potatoes in relatively clean condition for hand picking. The pickers put the potaoes in large baskets which a two or three man gang would then come along and tip into a trailer pulled in our case by our MH 25 or a Challenger for hauling to the clamp.
Joe - the time it's taken me to write this the spuds should be nearly ready - make sure they are nice and crispy on the outside - use a 220F oven.