So, I downloaded a Cass companion mod to see what it's about.

Mod Link:
https://www.nexusmods.com/fallout4/mods/19492

First quick to solve issue was the voice files. Simply open up the CK+LazyVoiceFinder and bink bank shaboom got the voices as well as named the correctly.

Voice Files Link:
https://www.mediafire.com/file/lab885nb796tafp/CassCompanionVoiceWAVs.zip

Problem is now I've been trying to get the voice to have lip sync, but the methods that I have tried don't seem to work. If anyone knows how to do this a link to a download for the .lip files and/or an explanation on an easy way to do this would be helpful.

Edit (for whatever reason the mediafire like keeps going though adfly idk why but i'll see what I can do.)

I was never confident enough with CK to get that one working, but if you're looking for an alternative, TheL0neW0nder made a mod that adds 4 fully voiced companions with lip synced dialogue from New Vegas, including Cass, as well as Veronica, Raul and Arcade Gannon.

Here's the link if you're interested.

https://www.nexusmods.com/fallout4/mods/56994

I did see that mod before. I think I avoided it because of the Project Mojave requirement, but I might test out bringing them to the Commonwealth and then removing the mod and hope not too bad of jank happens.

Thank you though.