As long as the Glock's dovetail cuts are the same or narrower than those of the Kahr, you can use the Kahr rear sight. Most likely, it'll work.
But that's not the real problem.
The real problem is the sight's height.
The height relationship between the Glock's front and rear sights needs to remain the same.
If the Kahr rear sight is lower than the Glock's, you will have to either file the Glock front sight shorter, or buy a new front sight of the correct height. Conversely, if the Kahr rear sight is higher, you will have to find a higher front sight for your Glock.
One normally measures these things with a micrometer caliper, not necessarily an expensive tool to buy. (I'm not referring to a screw-thread micrometer, but rather to a caliper. See, for instance: Sears: Online department store featuring appliances, tools, fitness equipment and more)
In the case of the dovetail, just remove the sight with a brass (or aluminum) drift and measure the width of the sight's base, front-to-back.
For the height, measure the entire thing, bottom of base to top of blade.