But they did believe in the gospel (Good News)!  It was not rhetorical question.  A way to understand the verse is to look at who the characters are, what time frame they are living in, and what could be a reasonable assumption of their religious viewpoint.

Let's look at other verses to try and put us into the mindset of Jesus and his disciples. 

Matthew 15:  24 Then Jesus said to the woman, ?I was sent only to help God?s lost sheep?the people of Israel.?,
Mark 7: 26 Since she was a Gentile, born in Syrian Phoenicia, 27 Jesus told her, ?First I should feed the children?my own family, the Jews.[k] It isn?t right to take food from the children and throw it to the dogs.?
   28 She replied, ?That?s true, Lord, but even the dogs under the table are allowed to eat the scraps from the children?s plates.?
   29 ?Good answer!? he said. ?Now go home, for the demon has left your daughter.? 30 And when she arrived home, she found her little girl lying quietly in bed, and the demon was gone.

In these two verses, one can understand that Jesus main interest was for Israel.  His focus is to help Israel, and he also puts Israel and the Jews over other religions  as noted in Mark 7 with the gentile woman.

Judaism, which was the religion of Jesus and the disciples, is set to heal the original soul - Adam - and therein would allow all the Jews  (could be read as everyone) into being accepted into the Kingdom of God for eternity.  The ultimate goal is to heal the world, not only the Jews.  As such by believing in Judaism, one could see the blessings of the One True God by the very nature of the old testament and the Jewish race.

While Christianity has interpreted this to be the Gospel of Jesus, I believe that it was more the Gospel of Judaism. For they believe that the Kingdom of God is always just a prayer or action away from becoming reality. Jesus is noted to teach in the synagogues, if he was preaching the Gospel of Jesus, I very much doubt that he would have been allowed to continue. You may also note that his miracles are almost all done with a saying about how the person's faith is what cured the afflicted person, it was not his doing. Which would lead to one believing that he was pursuing Judaism as the appropriate way to get to the Kingdom.

I think that your quote from Acts is what the Good News turned into.  Remember that at that moment in Acts, Jesus has already died.
The verses noted before where when he was still actively preaching. 

By Jewish religious law, the messiah could not tell or say that he was the messiah, for it is written that God will make the Messiah apparent to the rest of the world.  So, as he preached in the synagogue he could not state that he was the Son of God or the Messiah for that would have disqualified him totally.  Just before his death, he asks Peter "who do you say I am" and Peter responds with the affirmative messiah response that then becomes another prophecy fulfilled. No one else til just before his death has recognized him as the messiah. Do I think that he felt that he was the messiah, possibly, for he astutely manipulated the masses and those that came to him for help by using reverse psychology and telling them not to tell anyone how they were healed.  Which of course would lead to a wide spread rumor mill about this really cool dude who chases out demons. How else would they explain how they suddenly were cured? Jesus only tells each person that it was THEIR faith that cured them, not that he had any hand in it.

There were in those times, lots of faith healers, even today there are faith healers.  Does that make it any more or less special?  No, it shows that he was religious enough to understand what the power of faith can do through a person.  By preaching the good news as Judaism, then he was accepted throughout the land as knowledgeable, understanding and meaningful. He also seems to have the ability to "setup" how his followers will look at the world. After his death, then the Good News changed into his story as converts wandered away from the original meaning, as St Paul redefined the words in keeping with his vision of Christ.   

 

Paul, when you speak of the Gospel of Judaism versus the Gospel of Jesus, are you making the assumption that Jesus is not part of the Gospel. Better yet, that He is merely a vessel that was used to teach the Gospel?

Luke 4:16-21 Shows Jesus preahcing the Gospel and at teh same time declaring himself to be the fulfillment of that scripture. It seems to me that Jesus was talking about himself.

John 5:16-18 Shows people getting mad at Him for teaching about himself as part of the Gospel.

Matthew 9:6, 10:37, 11:27, 12:28, 12:40, 16:13-16, 16:27-28, 17:12, 19:28, 20:28, 21:27-38 (a nise parable), 22:41-45, 25:31-46, 26:26 Are all versus in which Jesus was teaching and or preaching in which he referred to himself as a significant part of the message. I left out a bunch more that can be stretched to say that same thing. I also left some out that I missed. This is also just form one book. If you would like I can go through mark, luke and John as well.

Matthew 3:17, 17:5 Even shows God doing a little preaching. The only thing God has to say in all of the Gospels, but not the only times he says it.

I'll agree that the general Gospel that is taught today is not the same as what was taught by Jesus at that time. However, I don't think the Gospel changed any.