This mod is pretty straightforward; it involves some exterior modifications to the WDP Angel minireg body. I was told this is commonly referred to as "featherlight" milling. The mod consists of removing a couple of the "ribs" which are positioned around the outside of the reg housing. Only some of the ribs can be turned on a lathe because the other areas of the reg housing hold threaded set screw ports, so that material cannot be removed.
At the time of this modification, I had a pair of Angel owners both request the mod right around the same period; I was able to pop out both modifications right back-to-back. I used one of my small CNC lathes for the mod, although the mod could easily be done on a manual lathe using traditional tools. The tool I used (seen in the pictures below) is a round groove insert with a width of 1/8" wide.
Here's the regulator bodies after the modifications were completed:
You can see in the pictures that the silver regulator has sharper edges on the outside. The green one was used on an Adrenaline marker but the owner of the silver reg wanted it to be modded as close as possible to the Adrenaline style.