You can get a Clark Weaver-style rib from Gil Hebard that'll replace the iron sights. It'll require some drilling and tapping...4 holes as I recall...but I think it's an excellent way to go. There are other ways to go as well, including a pure Weaver base.
First off, you will need to decide if you want the sight mounted on a frame mount or a slide mount. The frame mounting system will not require any changes to the recoil spring, mainspring or the load you are currently using as there is nothing attached to the slide changing its weight. If you go with a slide mount it is possible that you may have to adjust the recoil spring to a much lighter weight in order to get the slide to cycle properly with the added weight of the mount and the sight used or you may have to adjust the powder charge you are currently using to get reliable operation. In some cases a change in the weight of the mainspring is needed and the radius on the bottom of the firing pin stop is greatly increased to allow for a much easier slide movement when additional weight has been added to the slide. If you are shooting full power loads all the time then if you go with a slide mount you could run the risk of shearing off the four mounting screws used to attach the mount to the frame. It is possible to fabricate a couple of solid pins into the slide mount/slide to take the strain of the higher power loads off of the mounting screws but this is still something you should consider when making your choice. If all you are ever going to shoot are the softer bullseye target loads then the standard method of mounting the slide mount is not really an issue.
The Clark Weaver style mounting rib that Bob mentioned is an excellent choice for mounting a sight to the slide and is the one I most often recommend. This mount requires four holes drilled and tapped into the slide in a normal installation. The Rock River slide mount is also a very good mounting system and is a little lighter than the Clark unit becasue of all the extra cuts that are made in it for a greater number of ring mounting positions. The Rock River mount also has a set of cocking ears built into the back end of the mount for an aid in working the slide. The Rock River mount uses the same exact mounting system and dimensions as does the Clark mount. When mounting the slide mounts I will mill the underneath of the mount at the front end to fit over the front sight on a slide that has been originally fitted with iron sights. In this manner there is no reason to remove the front sight and by milling the mount to fit over the sight it still leaves a very clean installation and if you ever go back to the irons all you have to do is remove the rib and install the rear sight. Slide mounted sights will usually result in a little more sedate feeling slide action which some shooters like and claim that they are better able to get back on target for the next shot.
If you are going to go with a frame mount for your sight the only mount that I use and recommend is the one that is made by Caspian. This is a very high quality and rigid mounting system that is of light weight and places the sight back over the grip area and into the hand so there is no degradation in the balance of the pistol. The Caspian mount is a very nice looking mount with no real excess of material used in its construction and is the same one used on the Les Baer Bullseye model pistols. The Caspian mount will require that ten holes be drilled and tapped into the frame, five on each side, making for a very solid and secure system.
There have been several discussions in the past on this and other boards about which system is the most accurate, especially at 50 yards. It has generally been suggested that in machine rest testing the slide mount will be slightly more accurate at 50 yards especially if the pistol with the frame mount is used on a pistol with a slightly loose slide/frame fit. I will certainly not get into any arguments or long discussions about this as it has been thoroughly discussed in the past. It has been my experience that in pistols of relatively equal fit and in the "hands" of very high quality shooters that I have observed shooting both types of mounting systems both were more than capable of shooting outstanding scores at 50 yards and without a doubt the pistols could still outshoot the shooter in all cases.
In the case of sights used, you did not really specify what you were going to be using, I only use and recommend the UltraDot sights for bullseye shooting. Hopefully this has answered some of your questions about the mounting systems you have inquired about.
There is two more sight and mount systems that were not mentioned..They are the J-Point and the Docter sights.. Both of these sights mount on the slide in the rear sight dovetail..Generally there is no alteration to the gun at all but a melted instalation is available as an option..
Both of these sights are rather small and don't add much weight to the slide so no adjustment to load or springs is necessary.. They are similar and yet different, mostly in materals used in manufacture and cost,but both seem to be very good..I am using both of these sights and a couple of old Optima's and find that I like them more than the tube sights.. They change the balance and feel of the gun much less than any other type of red dot sight..
Just something else to consider..
Did I say that I like them ?? Guess so...