The duo missed last week’s home game against the Sharks due to injuries.
“We are happy to have Clayton and Raymond back as they will add to our attack with regards to our backline,” Duncan said on Wednesday.
“We are lucky enough though that the rest of the starting line up remains as it was for our game against the Sharks.”
Continuity was important for a Free State side desperate to get back to winning ways after 30-30 draw against the Sharks last weekend.
Although the Kings had not be convincing this season, Duncan said it would be a big mistake to underestimate them on their home turf at the Nelson Mandela Bay Stadium.
“They came close in a couple of their games and will pose a huge challenge. We need to stick to our game plan and focus on what we need to do right.”
In the only change among the replacements, Brendon Groenewald comes in for Werner Lourens to add depth to the lock department.
Cheetahs team: Clayton Blommetjies, JP du Plessis, Joubert Engelbrecht, Francois Venter, Raymond Rhule, Willie du Plessis, Sarel Pretorius, Lappies Labuschagne, Neill Claassen, Tienie Burger, Francois Uys, Henco Venter, George Marich, Torsten van Jaarsveld (captain), Caylib Oosthuizen.
Replacements: AJ Coertzen, Rudolph Botha, Brendon Groenewald, Vincent Jobo, Shaun Venter, Pieter-Steyn de Wet, AJ Coertzen.