In order to help you unlock my research....

looks like a vine/ tree that's grabbed the engineer?

Yes, ali81.

Ati was able to capture some of the text shown in Alien: Covenant and "plant" was mentioned in it (see below).

"If I read well David's lines on the drawing:

'Concurrent xenomorph development...'

'host sustaining functions and plant...'

After the word host (n) the word plant is not a verb, but a noun meaning the flower...?? That's why I wrote about the flower... I don't know, it's possible that I'm wrong.

The full sentences can't be seen."

the very origins of the deaconesque form in the mural?

Right again ali81. The blurry figure looks a little like a Deacon with a really bad head wound.

Looking closer, each side of the "head" appears uniform (similar dips on the edge) and the circular/oval dark colorations on the David 8 drawing seem to match (vaguely). It is tough to make out with confidence.

"From within each seed, comes the promise of a flower".

Most certainly IndyFront. Thank you for that. I'm one of the fans of Alien 3 too. That movie had such a strong cast.

Yes, the image does look a little like a bloom.

In the script it is said that a lot of David's wilder drawings are just his sick fantasies, not reality. He even draws one of those sick Shaw mutilation drawings in one scene, and she is long gone by then. This does not look like one of those, so this may be something real.

But David does mention some grotesque Engineer ritual. But probably no telling if he just meant the facehugger type of ritual, or something that we haven't seen yet, like with that face-plant thing.

I think he was probably referring to the sacrifice to create life in the first place, to spawn Neomorphs (Deacons; yes, they are the same type of creature) to while the slate clean, or (once they figured out how to weaponize it) the "atomization" bombing that we see David use in Covenant 

either an Engineer drew it or David redrew it. Either way i am happy. the evidence is their to for us to break down and with a little choped audio come to sane conclusion regarding it.

Two points i would like to make: "They thought sacrifice would cleans them of their sins"

what sins? those dipicted are 1 of them?

Also,  of the best of the best engineers  came the chosen one. this enhanced being would break down and give all he is to the planet. he becomes "their ways" he gets etched into mountains of planet 4 he is the best of the best. now a few hundred thousands years later his seed is more sour than ours.  so it must be cleansed. all that he was is over. a new god replaces the old?

wondered if anyone thought of that bit?

Absolutely great point sherris. I answered your question here.