To convert to discs or not convert? That is the question!

Right you are 65Val. It is indeed possible to lock up a non-ABS disk brake system. But that's the not the objective. The brake/tire combination is most effective at the point just before lock-up. Tires will be screaming at this point, but they'll still be turning. A turning tire is a steerable tire. No turn, no steer.

In setting up the bias on the brakes (balance between front/rear), most agree it is safest if the fronts lock first. This assumes, of course, that both front wheels lock at about the same time. Otherwise, the car is going to turn left or right rather rapidly. The problem with locking the rears first is that the tail wags the dog. Unlike Yaw under power, there is nothing left to bring the tail back into line.