Part of Mascis’ fuzz collection, as can be seen in this March 6, 2020 Marshall interview at 1:15.

Mentioned in this January 1986 Guitar Player interview, transcribed on the website of interviewer Tom Mulhern. The version is unspecified, but an eyewitness account of the V4 is given in this January 5, 2014 The Gear Page forum post by user Jumblefingers.

Guitar Player January 1981

I generally use a small pedalboard with a volume, wah-wah and fuzz. It never really mattered what types they were, except the volume pedal I used was the cheapest one, the first one I ever bought, in 1967. And until Roland out volume pedals in 1981, which are now the best I've found, I had to use the original one, which had a good on/off sweep. The Roland volume pedals let you adjust the on and off range. All of my electronic equipment is built into rack mounted modules by Tony Arnold of Arny's Shack. It's all custom equipment. He takes a small effect, builds it into a rack-mounting module, and slots it in. Besides the Roland Space Echo, I also have am Ibanez digital delay. The specific kinds of fuzz boxes I've used are Electro-Harmonix Big Muffs and Foxey Ladys, which were good – the old ones. You can't get fuzz boxes like that anymore; I've tried. All you can come up with, if you're lucky, are the old ones. Tony Arnold is planning to take a number of old buzz box circuits and put them all in one module with a switching rank, so you can switch around to any one of five or six traditional, old circuits. You can then go to Big Muff to Foxey Lady to Burns Buzzaround to Color-Sound and so on.

The Gear Page, January 25, 2014

I saw Fripp and Crimson many times in the early 70's and his small pedal board consisted of a Wah, Three Knob Guild Foxey Lady and a Volume Pedal. I had an original Foxey Lady back in the day and would like to try to get as close as possible to the original Triangle Muff/Foxey Lady sound with a new clone.