Greg Lake played a Rickenbacker for a very brief period, in or around 1974. I've only seen a couple of pics of it ever:
It seems modded out the gate, with a Jazz bass pickup cover over the bridge, revised control layout and custom pickguard. It looks like a mono 4001, which I think is unusual because it has binding and triangular inlays. Any thoughts?
I saw, and stole, an image recently on an ELP fan page on Facebook. Apparently this pickguard was discovered on a shelf, somewhere in ELP's offices. It looks like Danny O'Brien's work for Tony Zemaitis, and is clearly configured for a Rick neck pickup and a Jazz pickup in the bridge, albeit with the pickup much closer to the bridge than the stock Rick position.
I like the Tarkus inlay!
It looks like the pickguard never made it onto the bass, but it is a nice piece of work!