They haven't announced the qualifying process yet so the letters are just there as a guide really. I actually think Italy will be top seeds if they qualify. Montenegro will also be in the qualifying so it's 53 teams.
I'd say it might be 5 groups of 7 and 3 groups of 6.
8 group winners qualify. 2 best 2nd placed teams and 3 from the playoffs.
The last WC qualifers had 3 groups of 7 and 5 groups of 6 and the rest same as above.