Terminator 1 and Aliens were not shot in Super-35. They were shot mostly hard-matted (1.33 Academy, with a roughly 1.66-1.85 matte box in front of the camera lens). If you watch the trailers in 35mm unmatted, some shots are full 4:3, and some have black bars. The bars might even change size from shot to shot. There may also be FX animation that spills over into the black areas.
So from all I understand, full-frame home releases of those two were cropped to get a garbage-free 4:3 image. If you still want them, there were full-frame laserdiscs - I think the best-quality ones would be the first Image LD of Terminator (not the original Thorn-EMI-HBO, which may have been time compressed?) and the early 90s Fox Video release of Aliens (not the original CBS/Fox one)
For Terminator, look for the one with the poster art in front of a big picture of laserdisc - the standard Image cover art style of that era. For Aliens, look for the one with an all-black cover, no blue stripe at the bottom with the Fox logo.
To get true "open-matte" versions of Terminator and Aliens (with the in-camera black bars, and open matting for whatever scenes weren't hard-matted) you'd need a print. I know Derann sold full Super 8 versions of both (they also sold T2 - it was the regular scope version, and was apparently in mono, but it could be a good color reference.)