I'm also running an Age of Worms/Carrion Crown mashup in Golarion, combining aspects of Kyuss and Tar Baphon. Who are you picking for the Ebony Triad? I went with Asmodeus, Norgorber and Lamashtu. The Whispering Way and Cult of Urgothoa is pulling their strings.
We are in Greyhawk, so I kept it as is. Hextor (which worked very well against the Paladin and cleric of Heironeous), Erythnul, and Vecna seem to fit Greyhawk and the "old school" feel as well.
When the party made it to the temple of Hextor , they already had a bruising fight with the skeletons in the foyer, the guards in the foyer, and the piggy. The guards at the elevator had been bribed, charmed, and convinced that the Tiefling wizard in the party could make the delicacies of their homeland instead of the swill the temple of Hextor made for food. When the party made it to the arena, the head cleric tried to convince them to all come in. Sensing a trap the party refused, and there was a stand off.
The arena had a big statue of Hextor in the middle. The half-gnoll paladin of Heironeous walked into the arena, rearranged his armor and peed on the statue. This enraged the half-orc junior cleric of Hextor, and he launched himself into the pit to attack the paladin. The Paladin was surprised by this and turned towards the half-orc. I had the player roll a ranged attack roll. Nat 20. The half-orc was blinded; the cleric of Heironeous ran in and pulled the paladin out, and the normally regimented order of Hextor devolved a bit into chaos and fought the party on the party's terms (outside the entrance of the arena. The party was running on fumes; The head cleric was hard to hit and was about to heal himself when the paladin said, "I peed on your god." The cleric lost it and attacked the paladin instead and missed. One of the charmed Tieflings ran up behind the cleric and clunked him on the head to knock him out.
That was how the party got some Tiefling guards/muscle for their base back in town in exchange for keeping the Tieflings well fed.