I’m looking at building a mustang that I can race in the nasa cmc and also take it drifting when there isn’t any local road course events. Any advice for this build?

Considering the rather strict rules for the Class I would just dig deep into the NASA rulebook to see what you need. There are even specific issues concerning the roll cage, the thickness and other specifics concerning the safety of the vehicle. The NASA Region in your area is one of the best in the entire US so you might even reach out to folks there for a little advice and assistance in planning your car. Always good to do your due diligence so you don't purchase a bunch of unnecessary items but when building a Spec type Class following whatever organization one is running rules is the best format.

www.nasagreatlakes.com

Road racing and drifting are not mutually compatible. The drift car would not be good at handling and visa versa. The front suspension mods, involving spindles, Ackerman, caster rates and etc would probably make the car illegal in the road race class. Basically, you'll need to pick a discipline. Road race stuff, I can help you, drift..not so much