Thought I would get a few pics as I was doing an XM-L swap on a 120P I acquired recently for the inquiring minds. The pictures speak for themselves so I won't get too detailed here.
Here's the luck candidate.
Take off head and remove retaining ring. I found out a new trick to getting the stubborn ones loose, (thanks to CarpentryHero's Special Ops) my calipers ends are very strong, fit nicely in the notches and you can lock them in position. I learned this after a half an hour of trying to use snap ring pliers with a BIG . The calipers make it seem so easy now. Before you remove the old emitter check the polarity with a 3 volt source and mark the positive and negative outs on the module.
The trick here is to use the Datiled 8mm boards. The SSC P4 that is in the 120P is 8mm Diameter so this works out nice except you have to shim the board. There is a 0.5mm difference in height between the P4 and the XM-L/board. I had some thin copper shims at work I used to cut down to 8mm diameter.
The shims came up a little short at 0.34mm so I added thickness by soldering layers until it was 0.5mm.
Arctic Alumina down the shim and then the XM-L board. Before it dries slide the module into the head and check to make sure it's aligned in the reflector, adjust as needed. After it dries I use the leads from 1/8 watt resistors to jump the board contacts to the module output leads and solder the connections.
For some reason I just couldn't get it to focus on the emitter but it's good and centered. 3000k warm XM-L.
That's about it I guess,