It appears to be the Distillate electronics package (pickup switch, volume, filter, Q switch, quick tone switches (boost, neutral, cut) for bass and treble). A Signature of the period (presumably 1987) would have a decal of Stanley's john-hancock on the headstock. If the serial number has a D then it was ordered as a short-scale Distillate with a small standard body.
Love that Bird's-Eye Maple!