Since posting all the preceding, I have installed the second HID of the kit into my 1985 R80RT. The results were similarly pleasing and (despite my original intentions) completely unphotographed.
I made the RT installation in a similar manner to the GS, tapping directly into the power feed for the headlights, immediately after the lighting relay, and obtaining power for switching from low to high beam directly from the H-4 socket. Once again, I used a couple of short lengths of wire and avoided using most of the remaining portions of the supplied wiring harness.
I propose that this is the best installat6ion method, avoiding, as it does, the addition of several new potential failure points and a seemingly unnecessary and difficult to replace relay.