37th Ave West seems like a particularly tricky location, even if the terrain does seem to give some clues, as the area seems to have changed considerably over the past 100 or so years. C.P. Frank's Atlas of the City of Duluth from 1902 shows housing plots divided up for a 37th Ave west (circled in red with two major current street circled in blue) but nothing actually built. If the houses in the background were built later, they may have been lost to highway development.
  

While there never seemed to be an actual 37th Avenue West built in that north section near the Wheeler Athletic Complex, a 1939 aerial image shows that a group of houses used to stand just south of Wade Stadium on a street that, while at an angle to the other avenues, could plausibly have been designated as 37th Avenue West. This location seems to fit the details of the photo, as there is a rail line directly behind the workers with houses on the other side of the line. If the location circled in red is correct, they would all be looking north with this grouping of houses directly behind them.
  

I still think the location is likely to be somewhere in the upper left photo, amongst the residential buildings torn down for highway construction. You can see a few somewhat hilly areas that might match the topography of the photo, but even this photo from around 1950 is really too recent to understand what the neighborhood looked like when those houses were built. Streetcars no longer ran at that time and the Twin Ports by Trolley book notes that in 1940 Wade Stadium replaced an athletic stadium that had existed just to the south near 37th Avenue West. 

I did find two pictures related to 37th Avenue West. The upper right photo shows the Albert Olsen Grocery on the no longer existent Coates Street, near 37th Avenue West.

The lower right photo is a house at 3716 Coates near 37th Avenue West. So there definitely was a 37th Avenue West. Where those particular houses in the photo were in relation to it remains somewhat of a mystery to me. It does seem solvable though. Perhaps from finding a match for the topography in the photo or maybe even just having a proper translation of the Norwegian word “poo.”
  

Thanks, HBH1. In that hazy period between sleep and wakefulness this morning I had the realization that that one word might actually resolve a number of things. I’ve been trying to align the topology to find some location where those houses could plausibly be on 37th Avenue West, and have found some close matches for the houses, but for every house that looks like it could be right, some other element is clearly wrong. In all of this I’ve trusted that the labeling on the back of the photo is correct. 

But if that’s what I’m trusting, then I should trust it. It doesn’t say these workers are near 37th Avenue West. It says they are on 37th Avenue West. And they are working on constructing tracks, not building houses. So the maps and the writing above really have all the necessary information. According to the 1902 map, there are three places where tracks crossed the very short section of 37th Avenue West: the streetcar line and two freight tracks. And homes are visible in the distance, not water, so the general direction they are facing is also clear.  The streetcar line started operating in 1891 but those tracks are slightly elevated and there appears to be no street, so that suggests that the photo is from before 1891 and those are freight tracks, either running along 37th Avenue West or crossing it. The tracks crossing the avenue line up with the topography and the ones running along it do not. Therefore, I think it is most likely the location is the one shown below. The aerial image is from 1939, around 50 years after the photo was taken, which might explain the absence of the three key houses. Finding some evidence of those houses would be a nice way to confirm or reject this idea, but this seems much more plausible than the earlier location suggestion. In any event, it’s nice to see that the rail bridge over 37th Avenue West is still there, even if the rail is long gone.