LitR includes XCell, along with face-generation by VEFS. If you've added mods, and NPCs in those mods are missing heads, this is an indication that they need facegen data. This can be generated pretty easily with VEFS- The tool itself is actually dead simple to use, but the fact that we're 1) using a stock game folder, and 2) using a downgraded FO4 both make setting things up an annoying process.
Installing Creation Kit into LitR
The easiest way to install creation kit (so that VEFS can find the damn thing) is to add it a mod inside a root folder. Create an empty mod, create a new folder named "root" inside that mod folder, and copy-paste all the creation kit files into it. I did this by just sorting the folder by date, and copying what matched the date of the CK executable (because I installed the CK on a different day than I installed the rest of FO4). The version as of the writing of this has 970 files, inside a couple of folders. It's less complicated than it sounds, the whole thing only took me a couple of minutes.
Also, you need to copy steam_api64.dll file from your steam folder (so, the NG version of the file) and rename it to steam_api64_downgradeBackup.dll, and include it as well inside the root folder with the rest of the CK files.

Installing CreationKitPlatform
Download https://www.nexusmods.com/fallout4/mods/51165
Create an empty mod folder, add a root folder, copy all the files into it.

Installing VEFS
Installing VEFS is actually extremely simple. Just follow the instructions on the nexus page, and don't forget to override the steam app id. I recommend installing it outside your LItR folder so it doesn't get deleted when you update (or you can tag it with [NODELETE], that works too.)

Running VEFS
Disable the pre-existing Facegen mod (this may or may not be necessary, I've seen some weirdness with the files not generating when this already exists, not 100% sure though)
Literally just run it, with the face generation. When finished, the generated files will be in a root folder in the overwrite. Copy/Paste this into a new [NODELETE] Tagged mod.
If any of this isn't clear, hopefully the attached pictures of how things need to be setup should help