For some odd reason I'd always seen this bass as an 8 string, so last weekend I took the plunge (literally with a plunge router) and did the conversion. The first 8 string bass I ever played was a Bitch back in the early 80's, and I was really impressed by the BIG sound. To my knowledge BC Rich never did a Mockingbird 8 string bass, but this is how I imagined they'd do it. I used Hipshot Tuners all around, and a Schaller bridge. The combined string tension of the D'Addario string set is about 320lbs, which is right at the edge of what works for this neck. I'll check into the Kalium site to see what they have that might be a bit less tension, as well as SIT, who made the first set of strings I used on my custom Rickenbacker 8 string. Because that neck has two truss rods, it could take the higher tension of these strings (which are a bit beafier than the SIT strings), and probably more as the rods barely had any tension on them. This bass sounds really good, and I can't wait till Sunday's practice to see how it sounds with my band. Incidently, I relocated the rear strap button higher up on the rear of the bass, and it balances really well. In fact better than it did before.
they made at least 1 8 string Mock that I know of, it was up for sale a few months ago