Considering the idea of a bolt-on neck, using threaded inserts. Given the wedge shape of the neck seat, bolting on through a neck plate will require the neck holes for the threaded inserts to be drilled at a slight angle. I'm not sold on the idea yet, but we'll see.
Looking for likely neck plate candidates, I found this Beatles neck plate on offer via Etsy. Seemed appropriate as an homage to the original Beatle bass. Won't arrive down under until end of May, and even then might not get used. But if I go down this route ... this is the way.
Peter