So, what do we have here :
The neck has been replaced with an ebay-specials baritone neck, which I've defretted, filled the slots with thin plastic sheet (worked a charm) and coated with super glue. The fretboard feels a bit bumpy, I think I need to get a matching radius block (and find the radius first), and alternate new coats of CA glue and sanding to get it glass-smooth. This will allow me to lower the action, because now it's very high on the high notes, not that hard to play but not optimal.
The bridge is a plastic repro of some kind of cheap euro acoustic bridge, made for tailpiece -equipped instruments. I found a 7-string tailpiece that does exactly what is needed.
I like the look and the functionality of this bridge, the neck will need to be shimmed if I want to lower the action at some point.
I really love the sound of the fretless for quick arpeggios, combined with the flatwound strings it has a unsustained thunk sorta reminiscent of west African music. With the Sustainiac the slides between notes sound very smooth and fluid, even more woodwind-like. The bridge pickup needs to get closer to the strings, but I don't have screws long enough that fit in the mounting tabs, direct-mount pickups aren't usually supposed to go that high.
One last close -up shot to end this rant :
The copper tape under the bridge is there to ground the strings via the metal tailpiece, it didn't work that well because the wire poked through the tape, I used a Danish coin to press it against the tape, I could screw it in place thanks to the hole in the coin !