I finally found a second revision PCB, with an actual chip instead of the epoxy globs:
but, sadly, it doesn't have the X1 oscillator, so it can't be overclocked.
I'm being told that there is a third PCB revision with a proper GSU-1 chip (this one is still marked as MARIO CHIP 1) which might have an oscillator. So, could somebody open his Star Fox cart and verify? Please?