Re: the rear port cover in T1, it may have been a found part, but I've never seen anything that matched. I was able to get a REALLY good look at that Propstore T1 Explosion Endoskull when I went to Comicon in 2018. I photographed it from every angle I could (it was behind glass). But, I was able to get enough photos to run it through photogrammetry and get a good enough mesh to reconstruct it in 3D myself in Fusion 360. So, I'm nearly done with what I think is the most screen-accurate depiction of that part anyone has made to date. Others have tried, but I'm able to now see things that nobody gets right. It's actually a very unique part.
In the photos where Shane Mahan is sculpting the skull, that port area may be the same, or the part may have been changed/replaced later as they refined the skull. I believe the skull we see in these photos is not the final skull for T1, it has indented text on various surfaces, it doesn't have the indented CPU port yet, and there are even extra protrusions on the back underside of the skull that get cut off somewhere along the way (you can still see those protrusions in the photos of the gray endo parts laid out on the ground.
I say this, because I'm guessing they took this skull sculpt, molded it, changed more things, molded that new skull... not sure how many times before they had the final version we see in the film.
And I have screen grab evidence, that shows that the rear port has curved not straight "bars" that run across the center. It's subtle, but those lines aren't straight, there's an off center dip down and then back up.
That may have been from the part itself, or it may have been fabricated by SWS. It also has some funky curved latch looking piece in the center and some indented circles/screws in the recessed bottom that we cannot see without the ref photos I took from the Propstore auction piece. I think you can get a good idea of what that part really looks like in the film from that collage I posted a bit back, look at the T1 Explosion Endoskull detail in the upper right.
Whew! Anyway, sorry for writing all of that out.
-Dana