Going purely off of memory here, but I think HK was built for the Mandalorian Wars (not to kill Jedi). I thought Revan lost HK during the war.
The timeline really should be Jedi Knight Revan —> Darth Revan —> neutral Revan (can’t remember if he actually joined the Jedi again or just worked with them against Malak).
Of the characters needed, only HK would match the lore. All others happened after Darth Revan (although maybe you could justify Bastila since the player can choose dark side in the game).
Also, this doesn’t really have anything to do with George Lucas.