Don't cut that old slide. - Burris FastFire Reflex Red-Dot Sight Mounting Plates

Putting a Burris Fastfire III on a Glock is the quickest way to improve your ability to get bullets on target. It totally replaces your sights with an affordable solution. But too many people are hung up on "Co Resident" and "What if" Scenarios, making them the perfect "Tupperware Commandos" and spending money that is never needed.
The newer Glocks have the ability to accept Red Dots already, IF you want to buy a new gun.

I did a little different. I had the rear sight mount replaced with the mounting bracket for the Fastfire III, then (When I was sure the mounting base was properly centered) I coated the underside of the mounting base with 3 M 4200 Marine Adhesive. Then I mounted it to the top of the slide. 4200 is a combination Filler agent and adhesive for marine applications and as such is permanent. It is temperature insensitive, Chemical insensitive, and darn near permanent. And a great shock absorber for the base plate to Slide fit.

I am VERY happy with the result. I am sure you would be too.