Posting this here to document as reference for others, this is what I know:
The seller of the bass stated that they were selling it on behalf of Jason Newsted. This was confirmed by the person who made the bass as a "Shop Night" personal bass while working at Alembic and sold it to Jason Newsted when it was finished. Although the bass lacks a serial number and is not an official Alembic issue, it is still a beautiful high quality instrument that plays and sounds great.
Mint condition, no signs of wear or play
Spoiler body shape
Tummy contour
Mahogany body
Maple neck
Ebony fretless findgerboard
Brass hardware
Adjustable nut
Sustain block
Controls: volume/volume/filter/LED switch
Red LED side lights
Neck profile is thin and narrow (very comfortable and easy to play)
Electronics cavity very clean, everything is in order, only replacement is the battery connector
The bass is lighter than I expected (I'm used to 70s large body Alembics), perhaps the tummy contour contributes to that. The Bridge and tail piece are set near the bottom edge of the bass and at first I thought the wide spacing of the pickups was to facilitate greater tonal differences between the neck and bridge pickups, but I think it was more a modification to accommodate scale length. I'm not sure how it all works, but the fretboard only has 22 frets instead of the standard 24 frets, so maybe the lower placement of the bridge and tail piece was to compensate in some way.
So, it's not an official Alembic issue, but it's a very nice high quality instrument made by a former Alembic employee and owned by Jason Newsted. Please correct me if I have misstated anything.