After 2 previous tries, I bought a microscope illuminator from AmScope, Model LED-64-YK. Their current price is $79. It's nicely made...the body of the ring light is an Aluminum casting with a nice black paint finish.

The hole in the center is large enough for my 60mm Nikkor Macro lens to look through w/o vignetting. I bought a 67mm to 77mm adapter adapter from Bower (about $10). I cut off the 77mm threads and mounted it to the body of the ring light with 3 small screws and epoxy cement.

I found that "frosting" the clear cover over the LEDs made the light more uniform. I used 220 grit sandpaper.

Here are pictures of the completed project: