The Gibson 20/20 was only available from late 1987 and 1988. The serial number dates this one to November 1987, manufactured at the Gibson Nashville plant. On such a short production run there is not too much room for variance, but there is some. The 24th fret on many 20/20s has double fret marker dots, but that fret is just plain on this bass.
Hardware is not typical for Gibson. The pickups are similar to seventies RD Artist pickups, but they are not the same. These were only used in the 20/20. The Sperzel tuning keys are another unique 20/20 feature, as is the height adjustable nut. The Schaller adustable bridge is one feature that is a little more familiar.