The SRB-1 will not fit the standard Rickenbacker ring, no matter what online photos seem to show. The opening of the Ric ring is just 1 1/8 in wide. Per the SD website, the coil dimensions of the SRB-1 are 2.87x1.42 in. and the surround opening is slightly larger than that to allow the pickup to be raised.
One of the oft-repeated lies about the Duncan pickups is that they're just guitar pickups that Seymour is selling as bass pickups. That's utter bullshit, whether or not you like the tone. The SRB-1 has alnico 5 magnets under those blades, unlike any of Duncan's blade guitar pickups. It's just Ric fanboys running down anything non-factory. Not that I care, but Ric has used the same pickups for guitars and basses many times over the years anyway. And I'm pretty sure a pickup doesn't know or care whether it's being mounted in a guitar or a bass.
I've heard both the bridge and neck Duncans in a Rickenbacker, and IMHO they do retain the Ric sound. Then again, I didn't listen with any preconceived prejudice against them. And I like what I hear in Rob's basses. YMMV.