Conclusion (Before Reading Further):
Don't do it.  The Dial-A-Jet system is OK in theory, but in practice it falls short.   In rebuilding the engine with performance cams and heads, I left the Dial-A-Jet system in.  When we went to the dyno, we did a run with and without the Dial-A-Jet.   The Dial-A-Jet caused a 2 to 5 HP loss, almost throughout the RPM band.
On non-V4 bikes, I can see how the Dial-A-Jet may be useful.  It would allow you to run the bike really lean, and use the jet settings to richen it up for optimal performance.  Unfortunately, on our V-4 bikes, we have to remove the airbox assembly in order to reach the adjustments.  This is obviously time consuming, and defeats the purpose of being able to change the jetting on the fly.  So, in conclusion, for the V-4 bikes, the  Dial-A-Jet system causes a loss in power, and gains no adjustability over the stock setup.

The Dial-A-Jet kit promises correct jetting under a wide variety of circumstances.  It uses a jetting system that takes 'input' from the engine (vacuum, vibration, etc.) and determines the best jetting based on that.   How well does it work?  Well, the jury is still out.  I have installed one, and found it difficult to install.  The people at Dial-A-Jet were very helpful, and with their guidance, I managed a successful installation.  The jets need to be mounted in the rubber pieces inside the airbox.  Included in the kit is a great tool for 'cutting' through the rubber pieces to install the jets.
Looking at the jet to the right, you will notice the 'body' (the black part) and the feed 'jet' (the long brass part in the x-direction). This feed 'jet' gets screwed all the way into the body, and the end to the left sticks into where the carburetor air flow is located.  This is why you need a hole in the rubber assemblies.  The brass fitting sticking straight up is where the gas supply is fed in.   The gas supply is fed from the bottom of the fuel bowls with included adapters.
The difficulty arises in trying to mount the jet brackets.  The photo to the right shows both the 'jet' and the mounting bracket.  There are four of each in the kit, one for each carb.  The bracket on the right is as included in the kit.  There is no way to make this bracket fit in the airbox using the stock holes as instructed.   Also, because of the angles involved, there is no way to drill new holes to make these fit.  My answer was to cut and grind the brackets, to make them fit, the results on the left in the photo.
This worked OK to fit the brackets, but now that the brackets are inserted, there is no way to get the jets installed so that they clear the top of the airbox.  A dilemma!  This is shown in Figure 1.  Notice that the jet sticks up past the airbox top.  Not the metal piece, which will eventually be threaded in, but the black plastic piece.  take my word for it, there is no way this will easily fit!
Figure 2 shows the attempted installation using the brackets of all four jets.   This looks good from a distance, but in reality, once the jets are fully screwed in and installed, the plastic bodies (and in some cases the hoses leading to them) stick well above the airbox.  There has to be an easier way!  There IS!!