My information has it that all of the BRNO models with integral scope mount bases use the same size rings. I have Model 21's both with and without integral bases. I suspect the 21's which you saw with the ZG47 type safeties were transitional models, although I imagine the ZG47 bolt sleeves would fit either bolt.

Winchester had a fair amount of carry over in the transition from the Model 54 to the Model 70, and I understand some Model 70's were assembled with barrels marked Model 54. Similarly, there was a transitional period after WW II in which Model 70's appeared with the "clover leaf" tang pattern, but with reversed safeties.

Where are you located, and where did you see the 21's with ZG47 safeties? We see mighty few of them at all in my neck of the woods.