FWIW, the original greybox uses a 10nF input cap, yet for some reason, the YJM308 uses a 1nF input cap.
If anything, especially with singlecoils, you'd want that cap to be (a tad) bigger, not smaller!
I've built a few true-to-parts greybox clones (see PCB picture in attachment), own a 90's RI and an 80's serifed-font that sound nice.
Owned the YJM308 for a short while, but found it awful.
I've modded the 90's RI, with 5mm green clearlense LEDs as clipping diodes for more crunch and output, and a toggle-switch for the input cap (tight or full), depending on whether I use it as a lot of dirty boost (=tight is better), or just a gentle nudge of volume and Drive to min., which -when using singlecoils- sounds better with the fuller input cap (I think I used 22nF or 33nF). That *will* become bloated a bit with humbuckers though.
After experimenting with op-amps, the greybox uses LM(or UA) 741CN's, that are slightly hairier in tone than the TL061CP and LF351N.
If you're interested in the differences, see the attached Excel-sheet data image. I found that online years ago, forgot who the creator was, but my continuous image search/save (old Ebay sales in the early 2000's helped) of greybox PCB's all showed the 10nF input cap and either 2 ceramic disk caps or film caps for 2 positions and few different '741' iterations of the IC.