The first paragraph in my harmonization contains a sticky issue- the time at which the women arrived at the tomb. Mark indicates that it was "when the sun had risen," Luke says that it was "at early dawn," but John records that it was "while it was still dark." I decided that Matthew's version, "as it began to dawn," was a good compromise between the admittedly minor differences in details.
The second paragraph comes solely from Matthew, and I have chosen a translation which indicates that the earthquake occurred in the pluperfect tense, that is, it happened in the past before the events described there. I understand that there is a great deal of debate about the choice of this tense, but I decided to err on the side of harmonization, for the benefit of this exercise.
The third paragraph also contains a contested issue- whether men or angels appear at the tomb. A common argument is that the authors who describe men intend for their readers to understand them to be angels. Since only one gospel explicitly calls them angels, I decided to use 'men' as the description in my harmonization.
The fifth paragraph also contains a troubling passage- that of Mark, who records that the women were afraid, and spoke to no one. This seems to be in direct contradiction to the other gospels, which record the women as going directly to the disciples and reporting what they had seen. In addition, Matthew characterizes them as joyful, not afraid. I have omitted the Markan characterization, since I can find no way to resolve it with the other accounts. I conclude this to be the first of the irresolvable contradictions between the accounts.
From the sixth paragraph onward the Markan account ends, and I see a wide disparity between the other gospels after this point. There is a small amount of overlap between Matthew and Luke, but for the most part the accounts are vastly different, shown by the large amount of monochromatic text. The gospel of John is completely separate from the other two gospels after that point, and there is absolutely no overlap between them. It has been suggested that this phenomenon is caused by the lack of a Markan narrative for the other three Evangelists to base their final narratives on. Without this common narrative, a wide disparity between details should be expected.
The major contradiction in this harmonization is evidenced by the tears of Mary Magdalene, derived from the text of John. In the eighth paragraph, Mary stands outside the empty tomb, weeping because she doesn't know the location of Jesus' body. She speaks with the same two angels that were mentioned previously as 'men', and even turns around to see the resurrected Jesus, but doesn't recognize him. I find this behavior unbelivable, considering that in the fifth paragraph, she along with the other women see Jesus, recognize him, and worship at his feet. Why does Mary, having seen the risen Jesus so soon before (only the time required to run from the tomb to the disciples and back again), wonder about the location of his body, and even not recognize him when she sees him a second time?
The reason for this contradiction, I believe, is because the Synoptic gospels record the angel's appearance and the appearance of Jesus before the disciples are told and visit the tomb, while John records the angels appearing only after the disciples visit the tomb. Because of this change in narrative chronology, a harmonization illustrates this glaring contradiction.
I decided to end this harmonization with the ascension in Luke. No other gospel account records an ascension; Matthew ends with the Great Commission, and John ends with the nebulous suggestion that Jesus' ministry after his resurrection was productive enough to fill countless volumes with his deeds. The locations are also different between the three- John ends at the Sea of Tiberias, Matthew ends at a mountain in Galilee, and Luke ends in Bethany. I don't consider this a contradiction in the context of this harmonization- just a lot of moving about by Jesus and the disciples.
In conclusion, I have found one external and one internal contradiction in my harmonization. I am certain that a more rigorous analysis could show more, but it was my intent to be as lenient as possible. However, despite my leniency, contradictions are apparent. I hope that this exercise will be as beneficial to others as it has been to me.