It was a ridiculous design and spoilt an otherwise pretty decent arm. Given the absolute dominance of Linn/Naim/Bada at the time I think the intent was to lock cartridge choice to in house designs fitted by ‘approved’ dealers. If every single aspect had been followed they’d likely get alignment within a mm or so, but this means the arm board has to be fitted to the subchassis in *exactly* the right place to obtain the correct pivot to spindle distance. If not everything is out. There was a Linn tool for this (though it may have been Linn arm specific) but I’ve certainly seen dealers fit arms without it.
PS I’ve aligned an Aro by moving the arm-board by now, i.e. a two point protractor, the three arm board screws slackened of a little, and then a painstaking process of checking alignment, nudging, checking alignment again until it is ok, then tighten the screws without moving anything. A totally crap and frustrating way of doing things, but you have to work with the tools you have! It made me never want to own an Aro!