I converted the dash in my Duster from a standard to a rallye. I modified the sheetmetal instead of installing a rallye dash surround, and even did it while in the car.
Now, having done it, I would suggest buying a rallye dash frame and installing the rallye dash that way instead of modifying the standard dash frame. Much easier. But it can be done if you can work with sheetmetal. Most of the info is in the build thread for my Duster, the link is in my signature. There are a bunch more pictures of how I modified the rallye cluster. You also have to do some work to rearrange the wiring, you have to swap the wires in the connector for the gauges, as well as add an additional connector if you're using doing the swap into a later model car.
Before
Dash frame modified
Rallye gauges restored/modified
Installed