Okay guys, I stopped by the HARM today and talked with David William, the man in the know. Here is what he told me:
6880: This hull, with the flat transom, is the one pictured under the tarp outside the building. Due to rain earlier in the day and more forcast, not to mention the boat being in a very difficult location to get to, I was unable to take any pictures. I do know the boat was not modified to match the 7171
7171: This was verified to be the boat in the wearhouse shot in Detroit with the rounded down deck. It is currently owned by U-13 owner Dave Bartush(?) and stored in Detroit
7206: This boat, a virtual clone of the 7171, was painted in Atlas colors and used as a display boat for Atlas after it was retired at the end of the 1977 season. It was later aquired from Bill Muncey by the HARM, being sold not long after and shipped to Arizona. It was sold a second time and shipped to upstate New York. It was later sold for a third time, this time ending up someplace in Indiana.
Now, getting back to the round transom Atlas shown along the road with U-70 on the front cowl, there are only two possibilities:
1) It was the 7171 fitted with the 6880s cowl or with it's own paint changed
2) It was the 7206 while painted in Atlas colors for display purposes with U-70 on the cowl rather than U-71
I hope this solves the riddle of the Atlas since, as already stated, without knowing the date of that picture, we will never know which boat it was, other than NOT being the 6880