I've run the Hella lamps on my 69 for years, never have done the relay conversion but it is a great idea, as is running a big bypass wire from the alt hot lead to the battery positive to take most of the load off the amp gauge and wiring without completely disabling it.
I also put in the old BIG cop alt on mine which is nice, the brackets were the hardest part to find, the alt worked fine with the electronic voltage regulator.
The Hellas were one of the best lighting upgrades I have ever done, they put out more light with one headlight out then the old sealed beams did with both working, plus you can put higher wattage bulbs in any one that takes H4 bulbs.