If I was tasked with wiring this one up I would change the lugs, the ones on it are two long and just make it hard to get the wires formed neatly. Also the clearance between XO and X2 is closer than I would be comfortable with.
Lastly because of the bonding jumper and GEC that needs to go to XO I would need at least a 3 conductor lug.
I agree with the long lugs but if you look at the bottom right you will see that the X0 is already bonded with a strap going to the X0 buss that runs behind the other lugs, and find the terminal connected to this buss and you have your X0 which again I agree with Bob it the second double barrel lug from the left the small single lugs are H1-3 primary.
Also along with shorter lugs I would change to over and under lugs where one barrel is stacked over the other barrel as they are much narrower and you don't risk the X0 and X2 coming together as easy as it is now if the bolt was to come loose.
My guess (been awhile since I been in one of these) is:
From left to right:
X1, H1, X0, X2, H2, H3, X3
Taps I believe are + 2%x4 -2%x2 where at now is center 100% 4 above the center tap is plus + and two below center is minus -