I’ll be following this thread with great interest Kevin. I have a fleet of NJT and Septa cars from atlas I too would like to upgrade the interior and add LED lighting.
The interior photo you showed I believe is from a Comet V, judging by the larger windows and red seats. Now it’s your train and you can do whatever you like, however I think the Atlas cars are Comet 2s, which NJT refurbished a few years ago and they now have green seats I believe. Just commenting - feel free to paint yours however you like and you have inspired me to do mine now!