The unit can be seen at the very top of James's and Cliff's amp rack some time during touring for Ride the Lightning. The foot controller can be seen by James's feet at the Lyceum Ballroom in London in a picture taken by Ross Halfin dated 1984 https://i.pinimg.com/originals/51/8b/65/518b65b41a38a7bf8da28701ccb8d327.jpg

In this photo clearly we can see the Ibanez UE-400 unity over the Ibanez HD1500 an his golden footswitch

In a 1980 poster of the UE-400, it's mentioned that Sting is using it.

10th paragraph down and 13th line this processor is listed

In this image taken from REM's appearance on 2003's AOL Sessions, Buck's then-current effects rig is shown housed in what appears to be a monitor cabinet. The footswitch for the UE400 is visible on the left side of the board.

At this website you can spot the UE400 and Peter's settings (https://guitarpeterbuck.wordpress.com/about/)

"For this present tour, I play one large keyboard rack containing the PPG2, PPG1, Korg Polyphonic Ensemble (which I use only for strings), and the Arp Pro-Soloist. There is also a Conn Strobe Tuner for matching pitches. To my right I operate the Soundcraft Series 1S 20 into 4 mixer which takes both keyboard and guitar signals. For the guitar, which is a Gibson on this tour, I have an Ibanex UE400 Multi-Effects unit and an MXR Digital Delay. The Ibanex effects are controlled by a foot switch box with compressor/phaser/distortion/chorus/flanger and I set the guitar volume with a Boss pedal."

Mentioned in this January 1984 Guitar World interview, this March 1984 Musician interview, and this January 1985 International Musician & Recording World interview.

Guitar World, January 1984, "Carlos Alomar: Hard Driving Anchor Man For The David Bowie Show" by Gene Santoro

Alomar loves the concept of chimes, high frequencies, strange intervals and an odd bar of time superimposed on top of a very slick rock-funk format. Carlos' own guitar sound is a high-tech one, and any thing that he can pick up or throw into that to further its aims, he will do. He has everything he needs at his fingertips, and he signals the band with a nod of the head. Carlos will take a simple ninth funk chord and — before slapping it out — he'll slide up and down the neck, hit two dissonant intervals in between the funk and slap on his digital delay to make it sound like birds chirping. Then, he'll signal the band to go to the next section. Or, he might start off playing with the micro-synthesizer on, sounding like the guitar's under water, switch on the multi-effects with the sound of angels and then rip into an outrageous heavy-rock thing by slapping on some overdrive. This works out to the kind of sound, for example, he got in 'Fame': that is, funk chops all over the place laid over a clean, whack-flack execution; all kinds of cool chord inversions and substitutions; and the freedom to go wild with volume and sound effects through his mammoth rig of equipment in a huge stadium or hall.

Recently he has simplified his stage rig, and no longer uses the customized 700-watt system that in the past blew away the folks in the front rows. Now he plugs into two Roland Jazz Chorus Amps, with a Roland GP-120 that clicks in for solos. For special effects, he has two top-of-the-line Ibanez multi-effects digitals mounted on racks, and also uses two Electro-Harmonix micro-synthesizers. His favorite performing axes are his stereo Alembic, his 1958 mapleneck Stratocaster with a Kahler tremolo system and his new Steinberger six-string, which he was the first performer to introduce onstage.

Musician, March 1984, "Who The Hell Is Carlos Alomar?" by J.D. Considine, pg. 90

Carlos Alomar's criterion for his stage sound with David Bowie is fairly simple: "When I strum my guitar," he says, "I want to hear it come out of the amplifier just like on the record." To get that clean, well-manicured sound, he uses an Alembic stereo guitar, outfitted with Dean Markley strings (usually .009s), run through two Roland Stereo Chorus amps, with two Ibanez UE-300 [sic] effect units, a pair of Yamaha E-1010 delays, and twin Electro-Harmonix 203 guitar synthesizers. He also uses a Stratocaster, a couple of Yamaha guitars, and a prototype Steinberger guitar which he describes as "great, it's really great."

International Musician & Recording World, January 1985, "The Boy Keeps Swinging: David Bowie" by Philip Bashe

Carlos Alomar used an array of guitars: Alembic stereo electric, Steinberger prototype, acoustic, Spanish and 12-string. Amplification consisted of two Roland JC-120s and for effects, he employed two Yamaha E-1010 digital delays, Ibanez UE-400 and UE-405 multi-effects units, and two Electro Harmonix 230 guitar synthesizers. In this era of guitars that sound like every instrument but, Alomar opted for a fairly traditional and lightly textured sound.

"I didn't want too much of a synthesized sound," he explains. "I wanted to keep it balanced because of the horns on the album. And I didn't use the real heavy-duty power, because David's always screaming, 'No Heavy Metal!'"

Alomar played virtually all of the guitars on Tonight and details his unorthodox method of devising parts.

"I'll start off with the Alembic guitar and play one very complicated part, and from that I'll break it down into three parts and then play them all separately. This way you have your stereo placement: one guitar on the right, the other guitar answering on the left, and one guitar playing everything in the middle of the mix. It keeps the sound very interesting."