For all those wondering, here's how I did it to my SP and DRGW SD50s...

I used Evergreen #118 .015" x .188" styrene strip to build the headlight mounts on my DRGW and SP SD50s (.20" or .030" thick styrene would work also). I cut off two pieces of it, one about .275" long, the next about .090" long. I glued the short .090" section to the back of the long piece, bringing it even with the top (the assembly should have an "L" shape).

I glued another piece of styrene to the back of the assembly to help keep everything square, and to provide a place to mount microbulbs. I can't remember what the exact size was; I just cut and squared up a rectangular chunk of plastic to fit on the back. I glued a large piece of .005" styrene to the assembly (onto the bottom of the "L"), to hide the seam and provide a nice, smooth surface - this will be the top "cap" of the headlight mount. Once the cement dried, I trimmed it to the size. I cut a hole into the nose about .190" wide (centered left-to-right; use the nose grabs as centering references), and about .270" tall (as measured from the top of the nose down). I used my x-acto and needle files to CAREFULLY cut in the bevel underneath the headlight opening. I just eyeballed it until it looked right compared to photos.

If the opening is square, the entire assembly should drop right in, with about .005" or .006" of the "cap" sticking above the nose surface. Glue it from behind with some liquid plastic cement, then glue on either a Gyralite casting of choice (I used DA's), or a blanking plate for an SP, or late DRGW unit (the blanking plate is made from a piece of .005" styrene about .140 wide, and .240" tall, with rivet detail embossed from behind with a dull pin in a pin vise). That's it; paint it either black or scarlet, and if you took your time, there should be little, if any touch up needed to surrounding areas.

All of this is actually easier to do than I've described; the only thing to watch out for, of course, is the size of the opening you cut. As long as you follow the carpenter's adage of "measure twice, cut once", and don't go crazy with the x-acto and files, you should be okay. A miter box and razor saw (for cutting the styrene pieces), calipers, and sharp x-acto blades come in handy for this little operation. One more thing: if you plan on having working gyralites, you will need to trim back some of the weight in the nose to clear the bulbs (found that out when I tried to put the shell back on the frame ).