millercarbon
... but if you want something made "to specification" don't you need to specify the, uh, specifications?Perhaps he didn't provide the specs because he isn't asking us to actually build the armboard, but is just seeking general info from those with experience.
... The only other spec that matters is pivot to spindle distance. Which you solve very simply with a slot.Perhaps you lack the experience the OP seeks, because it's not always as easy as you suggest. Some pickup arms aren't designed to be mounted into a slot, but are intended to have a fixed mounting using just a few screws.