A thought on the Longer Ending of Mark

As we're studying St. Mark on Thy Strong Word, I referred the listeners to Acts 10 and Peter's sermon in the house of Cornelius. It is a remarkably fine summary of St. Mark, and fits very well with the solid tradition that though St. Mark wrote this Gospel, WHAT he wrote was the Gospel St. Peter preached. 

But then I noticed something that hadn't struck me before: it provides a fuller account of the events after the Crucifixion:

"....and made him to appear, not to all the people, but to us who had been chosen by God as witnesses, who ate and drank with him after he rose from the dead. And he commanded us to preach to the people and to testify that he is the one appointed by God to be judge of the living and the dead. To him all the prophets bear witness that whoever believes in him receives forgiveness of sins through his name."

It hit me that THIS comports quite well with the longer ending. He appeared to the eleven reclining at table (who ate and drank with him). He commanded them to "Go into all the world and proclaim the Gospel" (he commanded us to preach) and He promised that whoever believes and is baptized will be saved (forgiveness of sins through his name - the name put on us in Baptism). So I do assume that we have lost the original ending that Mark wrote for his Gospel, but I wonder if some faithful person in the early Church just put in its place another record of St. Peter's preaching, so that the longer ending may not be by Mark, but it IS Petrine (just like the rest of Mark's Gospel). What does anyone think?