The Pakistanis don't need any major weapons to stop the Soviets. The only route the Soviets face is through the Bolan and Khyber passes, each of which ar the worst terrain on the planet and also incidentally manned by a corps plus of troop........each, professional, trained and motivated troops. Air strikes in such terrain as experience has shown time and time again, are ineffective at high altitudes and suicidal at lower.
The only real weapons Pakistanis need are what they have plenty of and can be resupplied with easily, Arty,ATGMs and MANPADS.
Either way lots of Soviets are going to die. They have 2 options if they wish to attack. 1) move, cat 1 divs in E Germany. Thus is the only way they ar going to be able to break through the passes eventually. However this mo ement is going to be responded by US troops coming to Pakistan well before the Sovs are even ready. Now they face a war with the US. Option 2) maximum surprise, just employ troops in theater. That's about 8 divisions, in both Afghaistan and Tajikistan. To give you some idea, Cezchoslovakia in 1968 took 350000 troops in 50 divisions, and that was a much much much easier campaign then any in Pakistan promises to be. So the attack fails, and the Soviets have twi choices, either reinforce and face the Americans who are by nkw arriving or back down and admit they lost ro a third world country.
The sovs knows the above , which is why they did not do it.