Reading A, adjectival participle: καὶ ἦν χεὶρ κυρίου μετʼ αὐτῶν, πολύς τε ἀριθμὸς ὁ πιστεύσας ἐπέστρεψεν ἐπὶ τὸν κύριον.
In reading B, it's clear that all who believed turned to the Lord. That's also how I understand reading A. But some versions that translate reading A render something like "a large number who believed turned to the Lord" — raising the possibility that those who turned are only a subset of those who believed.Reading B, adverbial participle:καὶ ἦν χεὶρ κυρίου μετʼ αὐτῶν, πολύς τε ἀριθμὸς πιστεύσας ἐπέστρεψεν ἐπὶ τὸν κύριον.
This seems unlikely to me. I would expect a partitive genitive — something like πολύς τε ἀριθμὸς των πιστευοντων ἐπέστρεψεν — but I'd like to get some perspective from those with a deeper knowledge of Greek.
Thanks!