No help with your bass but I thought that I was the only person in the world who bought (and kept!) a Brawley... Mine is an SSH strat-ish guitar that I rewired.
Keith Brawley was an executive with Fender who had a lot of contacts in Asia (or just Korea?) so he had them manufacture a guitar that was designed with the open shark mouth headstock (which incidentally is being used on the Laguna guitars I've seen recently at the local GC.)
P.S. I have an active bass and thought that the preamp was to allow for shaping the sound actively (boost as well as cut) rather than just boosting the volume as with the preamps I've added to my guitars.
I really liked the EMG Afterburner I bought for $30 maybe 15 years ago but with it selling for $80 nowadays I'll have to pass on it. (I installed in a 2 knob PRS SE so I wired it up to a PP pot to switch it on to a preset boost.) Does anybody here know of any decent FET on-board preamps around these days - commercial or DIY? Thanks!