Where the characters from other series get the chance to be immortal, or deal with characters who are.
Stories are sort of sorted by series now. That is they are sorted alphabetically by the first series in the x-over, if the story is crossed over with a second series besides Highlander, you'll have to browse through the list to be sure to catch it.
No, it isn't ideal, but it is the closest I have been able to get to what I want.
The large Xover file was too huge. As a compromise, I am creating an All X-overs file - which has no summaries or character listings - but will be smaller and enable easy browsing for multiple x-overs. Smaller indices done alphabetically by first non-HL series, will contain summaries and character listings as normal.
All X-Overs
A - C D - L M - R S - V W - Z