Could be, they look like guitar-size blade humbuckers. OTOH Ribbecke's work was so limited and expensive, they're probably custom wound to his specs, whoever made them.
Ribbecke is semi-retired now, but he takes on limited commissions for $25K and up. Hey, no problem, where's my checkbook? He designed an acoustic-electric bass for Bobby Vega in the early 00s, called the Halfling, and AFAIK they're still made by the Ribbecke company but that's his daughter's company.