Well, I finally have my answer. I like the Barts, but they're extremely bright. I think the preamp was designed to boost treble and bass, leaving the mids more or less alone, and that the most neutral setting is with the treble and bass knobs halfway up. I've seen this on more recent active basses and it works well - when there's a center detent in the pots. The pots in this Pilot have no detent, so it's a bit more of a guessing game. I thought about swapping them out, but there are some funky things going on with the wiring (such as a trim pot for preamp output soldered on top of the bass pot) that I'm a bit nervous about touching.
Instead, I tried the same thing I did on my other Pilot (with DiMarzios): I put an 0.010 uF cap across the output jack, shunting some of the highs to ground. The bass now has a much more useable range of high frequencies, and it's an easily reversible mod. It's still a slightly mid-scooped sound overall, but the "clankiness" is gone. There's a ton of low end available but it's not boomy or muddy.
Comparing the 1989 SB-902 (Advanced) to the 1987 SB-602, the 902 is a tad heavier (maybe 8 lbs, so still reasonably light). The 902 has a slightly chunkier neck with more shoulder.
Pics coming when I've replaced a missing knob, probably today.