Robin - I would caution against too much 'attention' to nav co-ords. I have never conducted low-level heli ops as anything other than a 'joy-rider' but have fair experience of fixed wing LL ops. Such a nav system would NOT be used to the accuracy you are suggesting - the ops are visual, relying on visual features to navigate and any such nav system would be loaded only as back up, I'm sure. One might well use it to get into the general area of a waypoint but nothing else - in those days it would have been nowhere near accurate enough.