The Morley Power Wah Fuzz from the mid '70s is just an okay wah, but one of the gnarliest sounding splattery 60's style fuzzes ever made!
Unfortunately it has been misregarded as THE tone of Cliff Burton; and to the point that Morley re-released the pedal with Burton's name on it!!! The actual fact is that he used a Morley Power Wah BOOST and a Big Muff (most likely the op-amp version). And after you check out the demo below you'll clearly hear that this tone isn't anywhere near the first 3/best Metallica albums...
This is great demo that has been around for a decade now, but it's definitely worth a (re)watch as it shows just how ridiculous the fuzz portion actually is.
Check it out [the fuzzing starts at 2:49]:
thanks for watching!