Look at the first picture, you'll see how they're mounted. I cut a piece of SS from some scrap I had and bent/cut/ground it to the shape seen there. Then drilled/bolted it to the smaller gauge mounts on each side. The lightls shine directly on the face of the large gauges, not down on them, but I had to use a dab of clear RTV to diffuse the light a bit because it was quite concentrated.
The rings on the face of all the gauges I bought at a truck chrome shop here in Florida. They also have been on there for some years now. You can get that ring/bezel for the large gauge from Kuryakyn for about $25, or at a truck chrome shop for about $4. I have no idea what the brand name is now, been too long. This is where I got mine, about 65 miles up the road from me.
http://www.75chromeshop.com/