thats not true,
strut casings are identical, hence stub axles are the same.
brakes are different, with 86s getting (slightly) bigger pads, calipers, and rotors. rotors are also vented on 86 and solid on 85.
spring rates vary between models, but i dont think you'll be using original springs in pretty much any application
steering racks are interchangable between models, but swapping PS to non PS and vice versa can be problematic depending on steering column, and the cross members are different for the different types of rack also.
PS steering arms are longer than non-PS arms also (popular mod for drifters is to put PS knuckles on non-PS rack for more lock)
im pretty sure the PS pump and line setup is different between 3A and 4A too.