There’s plenty of material in the ERB corpus that needs only a slight twist: think of the rykors and kaldanes, the synthetic men, the planet men, or the realist and etherealist factions of Lothar. Ras Thavas might get along well with Dr. Benway.
No reason not to borrow from Burroughs’s spiritual descendants too: the atavistic drug shanga, Ramas’ mind-transference, or vampiric Shambleau hustlers. Living turbans from the Vaults of Yoh-Vombis would be all the rage.
You get the idea. It doesn’t take much and Mars gets a lot a more alien.