Nice machine Brad!
Hope you enjoy it.
Personally, the only Constellations I have are an 822 non-floater and an 822 floater..oh and a rather rough 862! Apparently, late versions of the 822 also floated, though I've never seen one of those.
Our range of Constellations over the years was not as wide as in the US but some models from the same era had similar model numbers. eg the UK 822 was similar to the US 82 in the same way as the UK 612 upright had similarities with the US 61, also differences, such as the position of the switch.
eg the UK pre-war uprights post model 543 had handle switches, then after the war, with the exception of the 160, 960, 262 and 912, there was a switch (don't laugh!) to foot switches with the 612, 638 and 652 The 61, on the other hand, had a handle switch AFAIK. I still wonder what all that was about i.e the switch to different switch positions according to country; what were Hoover playing at?
From what I can remember of my 822, the switch position is similar to that on your 851 but it's a wider pedal instead of a metal toggle.
Stephen