Picked up the book, So here is the long and short of it,

You must choose any Late War Tank Company (including those dirty Russians!) no mechanized company or infantry ect. one exception is the tank destroyer company found in Blood Guts & Glory. When building this company you do not have to purchase any compulsory platoons treat all black boxed platoons as grey. one platoon must come from any of the following areas HQ, Combat or weapons. Once you have selected a company you cannot change it, you can change the composition though.

First Round 500pts
Can only choose platoons from HQ, Combat or Weapons. 

Second & Third round 700pts & 900pts
Can only choose platoons from HQ, Combat, Weapons or Support.

For the First & Second Rounds of this campaign all Tank Teams count as Warrior Teams and operate as independent teams and can join other teams just like any other warrior team, here is the kicker TANK TEAMS ONLY so if the platoon has an infantry element or unarmoured vehicle there are removed from the field before the start of the game. There are also NO MORAL CHECKS. and Finally any Tank from your HQ or Combat platoon can be your Tank Ace. the Tank Ace can change game to game.

For the Third round, and the final battle its Flames as usual bar, any Tank from your HQ or Combat platoon can be your Tank Ace. the Tank Ace can change game to game any HQ tanks become normal tanks and your Tank Aces gets all the command Abilitys.

There are other things during the round but you will find out wen it happens, if you need more info to pick your force or are unsure of anything i mentioned in this let me know and ill try and get you clarification.