That is all correct, although I want to verify/explain that the predetermined alliances are based on who your partners are. Even then, it is not forbidden for you to "break" your alliance in one game; a stab, in-game and in the metagame with your partner if you will, for the solo is allowed.
If you are willing to stab one or both of your partners in one game in order to get a solo, that's fine. You will, of course, have to live with the consequence afterwards.
To continue with the hypothetical, supposed Zultar is England, 2WL is Russia, and Czech is Turkey in the first board. I, being England, can attempt to ally with France to fight Germany and Russia and I can also move on Germany or we can "fight" as to not give away that we are allies, either in game or in the tourney. If at one point, England can stab Russia for the solo, he's welcome to do so.
Gen Lee and Alderian do bring up a valid point. It might be tricky to convince one partner why you would want to keep another person in the draw, but even if you do, that *might* only reveal that you are partner with him/her in that round. However, you would not know who that other partner is in another game. So, there is a diplomatic process to this as well. You might have to argue that 3 way is better than a 2-way draw or whatever. That's part of the challenge and part of the aforementioned metagaming.
Part of my intention is to allow different sort of players to discuss the intricacies of the game because this tourney will include gunboat as well as diplomatic/press aspect.
As far as the "math" is concerned, a solo is better for the individual as well as the team. A solo nets 420

for the individual who soloed and zero for anyone else, so the individual scores 420

individually and the team, whose scores are 420 and 0, get also 420. A three way draw for a person with both of his partners, get him 280

while his partners get 140 each, so one person gets 280

and each of his team gets 280+140 or 420

.
In summary: if solo: player B gets 420, team AB gets 420, team BC gets 420.
If three way among ABC, player B gets 280, team AB gets 280+140=420 and team BC gets 420.