I'm not really wondering which one would be implemented...I'm wondering why they'd be implemented. I mean, sure they had invasion plans for Europe in the 1980s. But the US had invasion plans for Canada in the 1930s. It doesn't mean we were planning on using them.
There would be too much to lose. Those tanks cost a lot of money, and they burn a lot of gas. And when it's all done, the Soviets would be in charge of a radioactive wasteland that they're probably getting nothing out of.
At least in the 80s they were getting some trade concessions and SALT treaties out of the Reagan administration. Jesus, I just talked myself out of believing Red Storm Rising could have ever happened...
It depends on the mentality of the Politburo at the time. Certainly, there were times when NATO conventional forces were in danger of being overmatched. And a substantial segment of russian strategic thought included the idea that a nuclear war was winable. The russians might gamble that they can sweep aside NATO forces in place, and then present the west with a fait acompli when they try to strike back.
As for cause, this is a tricky one. Maybe another hardliner after Chernenko (any candidates?) who winds up looking for some way out of the dire economic straits the USSR is facing. Or the Soviets believe that an invasion is coming, and decide to resist with a preemptive strike (not that implausible; the Soviets did drill for that type of scenario, and had misread NATO intentions IOTL). Or maybe opposition to the Soviets in the warsaw pact (Solidarity in Poland seems a good pick, although the GDR makes a good flashpoint as well) erupts more suddenly and violently. The soviets try to put the rebellions down, and come to the conclusion that they are being backed by NATO... All in all, it is definitly not likely that the Warsaw pact heads west, but it is far from impossible.
On a side note, I believe that when Red Storm Rising came out, the one bit of the book panned as unrealistic was the method of starting the war, to which Clancy replied that there just werent any viable ways to do this.