That is a very nice gun, especially with the Volquartson trigger kit
The heart of the Volquartsen trigger kit is the
sear. They sell that separately. The Volquartsen hammer (part of the kit) is skeletonized. This supposedly reduces lock time, but it also reduces the strike force. I don't like it. The Volquartsen trigger itself (also part of the kit) has an odd curvature, and is not grooved. Again, I don't like it.
I used a Volquartsen sear, a standard Mark II hammer, and a Clark trigger.
The Clark trigger is no longer offered by Clark, but can be found on places like ebay. Stock up on them whenever you see them, even if you don't have a candidate gun at the moment.
The Clark trigger, being milled steel with tight tolerances, has squared-off front corners (where they bear against the pistol frame). This creates a small problem in the case of a Mark IV blued gun (with the aluminum frame). The trigger opening is rounded at the front, interfering with the front corners of the Clark trigger. The simple solution is to square off the trigger opening using a needle file. This is 5 minutes' work.
The stock undercut front sight is fine for target work, but is a "holster ripper" for anything else. I've found that the ramp sight for a Ruger Single Six revolver works well as a substitute. (Correct height, width, attachment method, etc.) If you're a perfectionist, you can match the bottom of the sight to the barrel profile of the bull barrel Mark by lightly grinding with a Dremel stone of the proper diameter.
Here is a picture of my Mark IV Target model, with the Clark trigger and Single Six front sight installed. Below it, from left to right, are the stock trigger, a Clark trigger, the stock front sight, and a Single Six ramp sight. The bottom of the Single Six sight shows how it is ground to fit the bull barrel profile.