The 4003 w/o the light rail is getting a little hard to find. I've got one from the early 90s. It is one of my favorite pistols save the Shorty 40.
Here is the one you are looking for:
Like I said this is my favorite pistol next to the Shorty 40, if you want a really nice concealable 40 take a look at the Shorty. They appear every once in a while. They are well worth the additional anti for a PC pistol.
The 4013 is built on the frame of the 4516, to my knowledge there never was a 4016. The 4003 was built on the 5900 series frame and the Shorty 40 built on the 6900 frame. These are smaller frames than those built on the 45 frame and much more concealable to me. One that still elludes me is the 4040, based on the 3900 series frame.
Cheers,
Sam