Biffo I'm sure others might have ideas on the illumination for you but spot/driving lights are usually used to supplement the main beams. I had a +4SS for a while which had the same arrangement as you and I didn't like it to have to switch the driving lamps separately. When I had driving lamps put on my 4/4 I had them wired into the main beam so they would go on and off at the same time. I personally would like to see if I could change this to that arrangement on your ARP4.
This is the best approach without doubt. Incidentally I am not sure of what technically is the definition of a driving light as opposed to a fog light. I mention this because it is illegal to drive with fog lights on when visibility is normal so I can imagine problems with plod if you drive with just the extra lights on.
