I think, that those can not be used. The units you named are more like unit types suitable for civ-specific unique units. You can have any number of mamelukes, any number of lancers. But there was only one Legio X, only one group of 300 Spartans, only one Bismarck. As I understand the concept, a legendary unit has to be:
1) Real. Some "poetic license" is probably allowed, but no Fictionalization.
2) Not only one specific person like general or spy. This is, what GP and Great generals are for. Unique machines with only one pilot are probably allowed as Red Baron is.
3) Unique. There was only one such unit in whole history - a completelly unique one or an outstandingly legendary instance of a generic unit.
as for the Lancers- I was think Napoleon's Lancers from the Old Guard. Or Even Old Guard Grenadiers. Another option for a UU would be the 95th Baker Rifles from that timeframe.