So a possible incipit of proto-Mark:
This incipit may explain Mark 11:27-33:The beginning of the good news of Jesus Christ, the Son of God.
In those days Jesus came from heaven to baptize John in the Jordan. And just as he was coming up out of the water, John saw the heavens torn apart and the Spirit descending like a dove on him. And a voice came from heaven, “You are my Son, the Beloved; with you I am well pleased.”
And the Spirit immediately drove John out into the wilderness. He was in the wilderness forty days, tempted by Satan; and he was with the wild beasts; and the angels waited on him.
After that John was baptized Jesus came to Galilee, proclaiming the good news of God, and saying, “The time is fulfilled, and the kingdom of God has come near; repent, and believe in the good news.”
When John was baptized by Jesus, John ''became'' Jesus.27 Again they came to Jerusalem. As he was walking in the temple, the chief priests, the scribes, and the elders came to him 28 and said, “By what authority are you doing these things? Who gave you this authority to do them?” 29 Jesus said to them, “I will ask you one question; answer me, and I will tell you by what authority I do these things. 30 Did the baptism of John come from heaven, or was it of human origin? Answer me.” 31 They argued with one another, “If we say, ‘From heaven,’ he will say, ‘Why then did you not believe him?’ 32 But shall we say, ‘Of human origin’?”—they were afraid of the crowd, for all regarded John as truly a prophet. 33 So they answered Jesus, “We do not know.” And Jesus said to them, “Neither will I tell you by what authority I am doing these things.”
The proto-catholic interpolator had to convert simply John in a baptizer and Jesus in a guy coming from Nazaret and not from heaven.
Secondly, the interpolator had to put John in the ''wilderness'' before his baptism by Jesus.