Bear definitely carved the plate. Casady claims the added magnet was his idea, I guess that's possible, but it seems more likely that it was Bear's. Who knows?! Bear built the electronics in that bass around a (likely modded) Gibson Varitone circuit.
The only thing I remember reading about was his use of a thumb pick in SVT, but I'm not a huge Casady-phile. In that pic it sure looks like he's holding a pick. With all the experimenting they did, it wouldn't surprise, especially in an informal situation like
this.
I always thought Jack was an active participant in creating his bass. I remember a show w/Airplane at Fillmore West in 1970 where, as they were setting up, Casady was clearly bothered by something sound-wise. He set his Starfire down on the stage, opened it up an began pulling out wires and adjusting things with his tiny screwdrivers. Like performing surgery. After a few minutes of this he reassembled everything and seemed happy with the results. This was the first I was aware of electronic basses. It sounded great, of course. My favorite bass sounds in those days were from Jack and Phil so it wasn't surprising to find out that both their basses had common origins; all those knobs...
