The simple fact that the Lukan version has an unbroken narrative as occurring the night of resurrection that includes his great commission to preach and his ascension contradicts the Matt. version. As I am sure you are aware that it is merely tradition that attaches names to these books. And modern scholarship has challenged these traditions quite persuasively when not conclusively. So again involving the book of Acts as proof that the writer of Luke knew something is not germane. The point stands that bible comentators have seen a need to place Jesus in Galilee when uttering Luke 24:49 (sometimes 47b-49). Why because they do not see how the phrase "abide in Jeusalem" could have been said before the Mattean Galilee trip without a contradiction. Also the surrounding sentences include the commision to preach to world which matches the conversation of Matt 28, there spoken in Galilee. The immediately following verse then shifts to Jerusalem/Bethany again. The text simply does not allow for this scene change. If we assume you are right and dimiss the views of Bible expositors, and understand that verse 49 was spoken the night of his resurrection in Jerusalem we must then say he was repeating himself in Galilee and the word "abide" means not "remain" but "return to" or "don't go any furthur than 100 road miles or so". This opens more problems, his apostles were yet doubting in Matt at jesus appearance to them in Galilee, which you say came after the account in Luke where we have them demanding proofs of identity (showed hands and feet, ate fish) the night of the resurrection and their faith is made sure. This is not the work of historians. This is legend making. I have offered a possible explanation as to why the two versions differed, that is to incorporate pagan god/man elements that the respective authors felt valuable to elevate their savior to the ranks of the other legendary heros adored by their contemporaries. But whatever you make of that it must be abundabntly obvious that the stories do not "harmonize" nor are they "complimentary". To make them appear so requires some unsupported redefining and artificial scene changing.