milli = 10^(-3)
micro = 10^(-6)
nano = 10^(-9)
pico = 10^(-12)

kilo = 1000 = 10^3

Often, the cap values are given in relation to microfarads, but the designation letters vary (m/u/mu). That's in line with Stratified's observations. For treble bleed circuits, the cap must be a few hundred picofarads, like the guitar cable.

>"The 600 appears to be the volt rating."

That sounds resonable, although this extreme rating is really something for tube amp circuits. For a guitar, the lowest voltage rating is okay, and consequently the caps can be physically smaller.

All I can say is that I don't know if there's a universal standard for cap markings. But if you're just one magnitude wrong (say 15 nF instead of 1.5 nF, that is 0.015 uF vs. 0.0015 uF), the tonal results will be extremely different.
Let the thunder roll and the lightning flash, I'm doing alright for country trash.