Andy, I believe I answered that question in one of your other threads. Detail Associates sells some great ditch light castings that are easily added to any equipment that needs them. For engines like AEM-7s and F40PHs you need to drill and file holes, but for others they can just be surface mounted.
David, I'm actually a little skeptical that the Microscale decals are the right size for the side numbers. If I remember correctly the AEM-7 numbers are smaller, or at least not as bold. Also, you might be able to use the red and white stripes from the Microscale set, but you'll have to mask and paint the blue yourself (Floquil Conrail Blue is close, and Modelflex Amtrak Blue might be a perfect match - never tried it so I don't know).
The blocky numberboard typeface used on some Phase III and Phase IV engines was Microgramma Bold Extended, sometimes also known as Square 721 Bold Extended. If you can find the font online, you could make your own decals in a word processor using white text on a black background. Font size should be 7.5 points. If you have access to a laser printer you can print them on regular decal paper, otherwise use inkjet paper. Just paint the numberboards white before adding the decals so the numbers show through.
Or, if you'd rather not make your own decals, I do know that Caltrain's F40PHs used to have this same typeface in their numberboards when in their older paint scheme. Microscale's 87-473 set is designed for these diesels, so it should include white numerals for the numberboards. As an added benefit, Caltrain's diesels are numbered in the 900-series, so the set might even include the exact number you want.
And speaking of engine numbers, I don't know which AEM-7 was the last to receive ditch lights while still in Phase III, but I can point you to the website of someone who might. He maintains a roster of the fleet and which paint scheme they're currently in, so he may also have the information you're seeking.