Check you model against the Version 2 pictures. 3rd Rail's version looks pretty complete.
http://www.keymodels.net/id23.html
Some things I will research are:
The cab awnings should probably be canvas colored, but could be black or aluminum and weathered. You should try to find photos of the engine number you have, they are all over the internet.
The most common thing I notice missing are the cab curtains, so try to find photos.
Next would be the warning light on the tender. 3rd Rail uses it as a backup light to pacify the 3 rail crowd, but I think it was a red warning light. (Unless it could display red or white.)
Something I will be working on is improving the lighting in the Layden illuminated number board boxes. I don't know if I should use mini LEDs or bulbs, but I will probably post when I find a solution.