I did finally get some correspondence from the seller, largely confirming what mtjam came up with.
Salient points - the battery compartment in this bass is underneath that engraved plate. The seller is reluctant to remove it for fear of damage I suppose,(understandable) but without an Alembic power supply box, there's no way to know if the electronics work. They are confirmed to be PF-5 electronics, with the humcanceller glued inside the cavity. If they are the 40+ year-old originals, they may require some work anyway. Hard to tell what kind of touch-up would be required under that brass plate, or after peeling that sticker off.
The best news, the bass is structurally sound. It's a legitimate early Series I bass from the somewhat formative years, and has an interesting neck wood recipe of mahogany, birch and walnut. Walnut back, and birdseye maple top. The case is almost certainly original.
It's a gamble, but possibly one worth taking. Just don't know if I could commit to a(nother) rescue. Gotta' think on this one some more.