The myths that the players know are real. There was (or is) a 10-year war between Heroic Kingdoms. An Adventurer-turned-King was engaged in an epic struggle with a Legendary Monster. The Emperor really does command the Sun. Omens predict unlikely outcomes for orphaned children. Touching the Rainbow takes you to the Plane of Legends. There is a Monster in that Cave.
Regional powers of gods
Only gods worshipped in that area are powerful because reasons (psychic power, spirits of the land etc); journeying far decreases Clerical power (is this curtailed from the top or the bottom? Do high-level spells fail and only simple magic remain, or vice versa?). DDG lists Greater, Lesser and Demi-Gods; if Demigods are local deities, Lesser Gods are revered through regions, and the worship of Greater Gods spans … continents? This would imply that it is the upper reaches that would be lost due to distance (lack of contact with local cult power-centre).
Clerics must take care that proper devotions are made to sustain their own powers, especially when far from home. Conversely, at their home Temple their power would be greatly increased (perhaps only in the Temple they Build Themselves).
Technologist as analogue of Cleric
Re-skin all Clerical abilities as Scientific Skills (healing/first aid, synthesising food and water etc).
Turning – against Robotic or Electrical Effect Zones; robots and computer security systems instead of undead – Holy Symbol is…
… hang on isn’t this Dr Who? If so, are we talking about Dungeons and ... Daleks?
Oh, that’s an interesting point. If the players live in a universe where Dr Who happens (semi-divine high-level clerics wandering about trying to ‘right’ stuff) that implies that the people who do that will come after the party. Because if the average party = Dr Who (as in, the parties are the 'heroes' in world-historic terms, not just in their own narrative), then the universe is in trouble.