I run Meth on my N/A 427, if you follow the install you'll be fine, however are you having Kr??
It will make the car run rich, afr on my car went from 12.7 to 10.9 before the tune, and IAT tune. after I tuned it I set it to 12.3. IAT's are great and I'm running WW fluid, I will do another tune when I start running Meth.