Doom for iOS level changing.

So I've recently taken up playing the Doom release on the AppStore out of boredom and nostalgia.

Of course, having beat the original countless times years ago. I pretty much breezed through the levels.
So, using iFile, I switched the .wad file with the one for Doom 2. Which, to my surprise worked rather well.
But again, having played these levels countless times, they posed no challenge. (And reminded me how bad some of the levels were...Really, 17-Suburbs?)

However, having never gotten far in the 2 Final Doom levels packs, I tried transfering them next.
This time, the levels loaded...but the textures were mostly missing.
It had always been my understanding back as a kid playing with level editors, the textured were also stored in the .wad files.

Google provided no help (support for iPhone games is still laughably small, GameFAQs iPhone section is a perfect example of this.)
The only things I found in my searches were an old forum thread with a dead link to a tutorial, followed by people thanking them for allowing them to play their favorite old custom wads, along with screenshots showing off obvious custom textures.

Is there some trick to this besides uploading the levels packs and renaming them? Or am I missing some key detail here...?

 

Of course. No reason not to jailbreak! lol
But yes, just get the official doom2.wad from a copy of the game. (The Doom collections only like $20 on Steam.) and transfer the .wad to private/var/mobile/Applications/Doom/doom.app/base directory, rename the existing doom.wad to something else. (Or just delete it, I
keep it to switch between levels pack. I'm currently attempting a Nightmare run. It hurts man.)
Then rename doom2.wad to doom.wad (caps matter. all lowercase.)
And play.
Just note that the level selection breaks, you can only select the first few levels, but all levels work in progression, or using the idclev## cheat.