What was inside those wedge-shaped boxes originally, and what repairs and changes were made? I don't know. But if we assume that they were from the Tonebender MkI schematic, we still don't know how gated and fuzzy these things were. Listening to Page, Ronson and Beck, they would have wanted less gated and less severly distorted, I think. So fiddle about with the resistors on Q2 and Q3. I found it very hard to get it to sound smooth, so go for very low gain transistors and vary your biasing. If Q2 is high gain and well biased, Q3 will be massively overdriven, since the FZ-1a assumes a lot of gating on Q2. So a low gain well-biased Q2 may be what you want here.

The Fuzz King, with a small change, does a pretty good "Communication Breakdown" impersonation, the standard Tonebender II is slightly too distorted unless you roll off the guitar volume. Although there may be less gainy Tonebender II units around. The 3-knob is a good all- round Yardbirds pedal although the fuzz quality is slightly different, the tone knob helps. My homemage Page 1 isn't bad, you would keep the Fuzz/Bias in one position and only use it to compensate for room temperature. I didn't put the tone knob onto my Page 1 "copy".