The original timeline reflects its Cold War period origin. Of course, the fictional timeline diverts from our own politically with the fall of the Soviet Union. The weapons and tactics that would have been part of the conventional war differ not only because of the loss of the threat of the Soviet Union but also due to the real world conflicts in Kuwait/Iraq, Somalia and the Balkans.
So what reference material is available? There are the original source books by GDW but that is not really enough to identify modern figures and vehicles, nor how to paint them. Well you have to make a decision about what is the base background.
My thought is that without the conflicts listed above, that there would be a no major developments outside those effectively predicted in the source books. So there are the signature "future" weapons such as the M1A2 Giraffe.
This means that the choice of factual source books should be limited to either those published at the same time as the game, or those that cover the period before the major divergence.
The company Tankograd publishes a number of books about exercises that took place in that period, such as "Key Flight '89" which was the last BAOR Cold War exercise.
There is also a book on the 1987 Franco-German exercise "Bold Sparrow".
There is also a few books on the vehicles in use in this period, such as the ubiquitous M113, specifically that used by the Bundeswehr. I have an Empress one that will be used by the Under Fire Bundeswehr troops for Twilight 2000 games.
Osprey published a number of books in this key period, their old Vanguard range is no longer available, but occasionally turns up in charity shops and other second hand sellers.
Their Elite series includes books on Warsaw Pact forces (Elite 10), Soviet Army (Elite 12 - originally titled "Inside the Soviet Army Today"), The British Army in the 1980's (Elite 14), Nato Armies Today (Elite 16) and Tank War -Central Front (Elite 26).
The Canadian Major looks like an extra from a car insurance advert...
Their Elite series includes books on Warsaw Pact forces (Elite 10), Soviet Army (Elite 12 - originally titled "Inside the Soviet Army Today"), The British Army in the 1980's (Elite 14), Nato Armies Today (Elite 16) and Tank War -Central Front (Elite 26).
