Wiggy if youre going to go ahead, I saw on one of the UK forums (sorry I'm on another pc at work so don't have history at the moment), there's a pinned thread with a wiring diagram mudmap of what is changed to include a relay across the headlights switch. I too plan to do this, (plus one for the heater  fan) later when I change to the 1600 GT dash. Having a basic wiring diagram will help adding the relays, and I'm pretty sure like Accapmad's instal, it's just an addition to the loom and reversible if you ever need to.
I have a shed to demolish, build and refit out  before this project gets to the top of the list.
 

I presume this Capri is the one from down Moss Vale. It is good you found the plate. Are you using the later facelift dash or the original Mk1 version.