Well there are no lavs on 77W between Door 1 and 2. Whereas sCO 772 has 3 lavs, 1 by Door 1L, and 2 before Door 2 and a closet. So it's not a fair comparison between the 772 and 77W floorspace.
That would mean that you're potentially only fitting those 8 rows of Polaris in the same space as 6 rows of sCO Diamond. That would suggest a guaranteed cut in Y seats for 30 Polaris on the 763, even with a reduced pitch (which lets be honest, what are the odds UA won't reduce the Y pitch?!)
No reduction in seat pitch in Y. Polaris configuration will be 30/184 just like the current 2-class 763. Seat configuration has been in the flight attendant manuals for over 3 months. CALTECH is correct - it is 1-1-1 in Polaris but really a highly, if not extreme
You can't compare sCO 772s to 77W as there are lavs, galleys, closets in differing configurations.
At first glace it does not look very optimistic for the 772. But, my guess is UA will add two lavs in front of 1L like the 77W, picking up space for larger footprint Polaris. E+ has 34" on the 77W vs. 35" on the 772 - 34" would pick up 7 inches - heaven forbid going to 30" in Y would pick up a lot more.
The answer on the 767 may be the number of seats across. 4 vs.6 on the 772 (66.667%) is 3 vs. 5 (60%) means there's more aisle space on the 767. My guess is the Polaris seats on the 767 will have the angled seats at a slightly greater angle, shortening up the length of the sets of seats.
787s seem to me to be a problem as they are about the same size as sCO 767 seat. The seats can't be angled further as there are 4 across like the 777. Maybe drop an F lav on the 788, but 789 needs 4 F lavs to match others in the fleet. E+ on the 788/9 could go 34" pitch and maybe lose a row or 2 to Y - that would pick up about 15 inches.