Hand-written note with Kurt's settings for the Polychorus (for Heart-Shaped Box and Radio Friendly Unit Shifter): ehx.com/blog/ehx-tone-tips-the-sound-of-nirvana
Despite the different names, the Polychorus and Echoflanger had the same internal circuitry. Kurt supposedly only had one EchoFlanger, despite what is said in (32). Kurt used the EchoFlanger on the Brazil shows (source info? Rio perhaps?) and the song "The Priest They Called Him" (found on various bootlegs, etc.). Both pedals were taken on the "In Utero" tour.
The EchoFlanger sometimes "acted up" and Earnie gave Kurt his PolyChorus as a backup. This PolyChorus was used on "In Utero" for the "Heart-Shaped Box" solo, "Radio Friendly Unit Shifter," and "Scentless Apprentice". Earnie sent out another PolyChorus to Kurt, hoping to get his back, but the "new" one broke and was given to Eric Erlanderson of "Hole" who had it fixed. Earnie did eventually get his PolyChorus back, but not before Kurt marked his settings on it with nail polish and put Velcro on it.
Indeed, Adrian Belew noted in some mag interview that he had an Electro-Harmonix PolyChorus that he'd had a technician remount on a stand and I think rewired to reduce AC and line noise. I think Fripp had one too. I wanna say it was a Musician article circa 1984 that covered Crimso gear or at least Belew's. The switches in my PolyChorus are poorly built and fall off a lot if not handled gently. Electro-Harmonix made some of the cooler guitar boxes of the late 70s and they are manufactured again after being rare for years (EH went bankrupt and another company bought the rights and designs since) but they're pretty expensive now. Their MemoryMan 16-second analog delay was I think the one oft referred to as a Fripp-in-a-box. Pretty sure Belew had an EH-7700 Polychorus flange/chorus/slapback echo/filter matrix.