This cheap ass version came with BC549C transistors known as one of the common high-gain transistors. The original B&M fuzz seemed to come with BC184C silicon transistors. and, I believe there were few different transistors Sola Sound tried at 70’s for the original B&M fuzz.
I replaced the components one by one to see the difference one by one. Omeg pots and 470pf caps made a improvement while NOS 0.1uf Mullard trpical fish didn’t bring a noticeable difference.
Most of the resistors are staying on the circuit board except for 3 of them. cheap ass version came with 3 different resistors than the normal and expensive BUM fuzz. you’ll need each of 100 ohm, 100K, and 33K resistors to revert this circuit to 70’s style. (or expensive version of BUM fuzz). 100 ohm resistor can be replaced with 220 ohm or 0 ohm as well. I’ll check the resistors and update later.
ZTX109 brought a tonal difference anyway. this bum fuzz sounds a bit older and bit alive than the original state with BC549C