Do the Stage VI heads use RC9YC plugs?

Not sure, since I don't run Champions. You can look for what crosses in Champs to Accel 113 or Autolite AR53, which are what I run.

The RC9YC is the same type of plug that I use in both the Eddy RPM heads and the Indy SR heads as well as I think they will work in the B1 as well as I have used them in the B1-BS heads They are a 14 MM plug size with 3/4 reach and 5/8 plug wrench size with a gasket and a protruded spark plug gap I have never ran any of the Mopar Stage 6 heads so

I have used autolite 63 for years the AR54 was too cold and would foul too easily at least in my motor

The AR53 have a 13/16 wrench size and the AR3923 have a 5/8 wrench size but all the other measurements are the same. The reason I listed the Champion number was I couldn't remember the Autolite number I used with the Eddy's in the Challenger. Oreilly's didn't have the AR53 so I am going to use the AR3923.

They worked great in the Challenger and the motor I'm putting in the Daytona is almost the same. I'm using the same cam but instead of the Eddy RPM's with a Victor 440 it has Stage VI's with an M1 with a custom Dominator, same compression.

Thanks