I have drilled and slotted rotors along with ceramic pads on my 86, but they were on when I bought the car so I can't compare to the original config. I'm no abs expert but as I understand the premise of abs is when one or more wheels break traction while braking the abs system kicks in. If you brake hard and don't loose traction on one or more wheels, it's not going to engage the abs as I understand. I think if you want to test it you're going to have to stage the situation, like brake hard on sand, wet pavement or something like that where it will intentionally cause braking inconsistencies between the 4 wheels.
I've only had a couple of times where I've stood on the brakes hard and there was no loss of traction on a wheel and have not noticed the abs engaging. Mine will stop hard and straight on dry pavement so I can't say how the abs reacts to that.