Whooooops! Say what? Who has ever said that? Certainly not anyone I have seen.
>>It seems someone did a whole lot of "theologizing" to omit water baptism and repentance from the conversion of a believer.<<
What???? Where are you coming up with these? The preaching of the Kingdom does NOT mean going back under the Old Covenant.
The Jews (along with them the 12) were still of the mindset that Jesus would return forthwith to set up His earthly Kingdom. Study the actions and words of Peter. He was still concerned with eating with Gentiles, eating no unclean food etc. Remember that Christ had told them NOT to go to the Gentiles but that He had come to the lost sheep of Israel. It was NOT until after He had ascended and the Jews as a whole still rejected Him as their Messiah that Paul was sent.
I'm having a difficult time understanding why you don't see the difference.
I asked at what point was the kingdom gospel shelved for grace and grace only? Do you see it at Acts 3 (which smvoice hinted at), Paul's conversion? Acts 10? Acts 15? If not clear in those points in Acts would it be safe to say that Paul did not preach the kingdom gospel in Acts 28?