It's a Electro-Harmonix Little Big Muff with the rare Op-amp circuit.
Up until 1978, the traditional Big Muff circuit used four transistors.
But in an effort to reduce costs operational amplifiers were substituted. These versions can be found
in the V4 & V5 PCBs. Model Numbers: EH3003A, EH3003B, EH1322, EH1322B, EH3003.
Some of the same circuit boards used in the Big Muff V4 were also used in the Little Big Muff
The Big Muff has 3 knobs: Volume, Tone & Sustain. The Little Big Muff only has a Volume knob.
Thus its a version 4 or V5.
Its the Op-amp version.
Thus the date : The 40th week of 1978
"I am including this as a legitimate Big Muff, even though it was not built on the classic Muff four-stage circuit. It was intended to sound like a Big Muff and was released in the same box as Version 3, so I feel it must be included as a true Muff version. Plus, I, and many others like them. It has a huge, crushing Big Muff sound. Though not quite the same as the organic transistor tone, is was very unique. Supposedly only a few thousand of this version were made".
"Version 4 is likely the Big Muff circuit heard on most of Smashing Pumpkins' Siamese Dream and Pisces Iscariot albums, so that should give an idea of the potential of this version. This is the rarest of the two op-amp Big Muff versions".(KitRae.net)
Electro-Harmonix Time Line
KitRae - The BigMuff OP Amp version