18DAI,
The initial guns were all Model 645's. That's all they made at the time. As time passed members of the unit started buying 4506's and then some of us purchased the 4516's for back up and off-duty. Several years before going to the Glock the city purchased Model 4566's for everyone in SIS.
None of the guns had light rails. Several folks with big hands liked the black rubber grip panels. I think most of us just used the original grips that came on the gun.
I liked the balance of the 4566's the best. I purchased more than one 645, only have one left---it's been around the block a time or two!!! I also have a 4506 that I carried usually between the front bucket seat and center console-so it would be near my right hand. Hard to present a holstered pistol while seated in an undercover car, wearing a shirt over the holster and often haveing a seat belt on.
We actually had several attempted carjackings of members of the unit over the years. Suspects would see a nice new car with one or more people in it and decide they wanted it at gun point--never worked out the way they wanted!
My original Model 645 is the gun I carried the most, it's also got more rounds down range and more tales to tell.
The whole unit starting carrying the Glock .45 approx. 2003. The Glocks were city issue, everyone got two. No one was carrying S&W .45's in SIS when I retired in 2006.
As I indicated in a prior post they can carry Glock .45's or 1911 style .45's now.

JH