JakeJonesIV on the iidb discussion group has offered the most coherent and contextualized explanation of the identity of Alexander and Rufus I’ve heard yet. Check out his posts 4292918 and 4291566. The explanation relates to Robert Price’s comment in his Pre-Nicene New Testament suggesting the possibility that Simon Magus is the figure behind Simon of Cyrene.
Note added 21 April 2023: those forum posts links no longer work so here are screenshots of them:
Wow, I love it when I read of an idea I have often wondered about being picked up by someone else who has obviously wondered the same things, but then gone on to develop that idea in a way that forces me to start reading the basic text again from scratch.
John Carroll does not allow for the young man who appears in the tomb at the end of Mark’s gospel to be an angel.
He is not an angel, as some have speculated; if we were, Mark would have said so. (p.127 of The Existential Jesus)