MSD 6AL function S4 Rx7
 

How would I go about being able to use the 2 step rev limiter function of the MSD 6AL on the stock FC3S S4 coil packs?
Would I need one 6A and one 6AL or both AL?

Search in the drag section. This has been covered. Basically you use a 6al on the leading and use a relay to turn off the trailing while on the limiter. Or, if you want/need the CDI on the trailing, you can use multiple boxes.

Okay thanks! Maybe I could use a RPM activated switch that I could toggle

Or you could wire one of those " well priced" shift lights to a relay for your trailing coils. Set it at the same RPM as the 6AL and just run the 6AL on leading coil.