The 2nd and 3rd gen PT-145's have the light rail. I haven't seen any other Mil-Pro's that have it but someone on another forum claims to seen a PT-140
with a light rail.
ALso another difference between the 2nd and 3rd gen is the recoil guide rod. The end of the rod has a larger dia head with a coresponding larger hole in the slide.
My collection of Mil-Pro's. 2nd and 3rd gen PT-111, PT-140, and PT-145's
Dallas Jack