This concept is silly and uncharacteristic and no amount of decent writing is going to get around that. If the year is 1968 they've been fighting, outside of American culture, for somewhere between 10-20 years. This is pretty ridiculous even by TF2 standards, and the fic presupposes this as if it's not weird at all. It's obvious that this fic was written just to talk about music, and, even though it mentions real history, ignores what would ACTUALLY be happening with the TF2 cast. Also, 1968 is obviously just used as Hey Jude's release date, because any other consequence of it is just stupid. After over a decade (or two) of fighting, acting silly on the battlefield to music they just heard is probably one of the last things they would care about. In all, what you tried to make imaginative and different just comes off as short-sighted and self-fulfilling. Try again.