There's a fair amount of online discussion about the guitar versions - evidently when Fender took over, the magnets were ceramic, but they changed them back to Alnico magnets. No word on whether the bass pickups went through a similar change. But I do have faith in Gretsch pickups in general.
If they're good in your Gretsch hollowbody, I suspect they'd be good in the Univox. You and I both share a preference for a classic 60's bass sound and well-aged flat strings, don't we? They'd certainly look great in that Univox.