[Kevan]

Depends how you define American muscle, it's much easier if you restrict to a certain era i.e. 50's/60's hard top.  When we had an A.M. class we had people racing modern open top sports cars because 'it's got a big motor and it's a muscle car isn't it?'

Likewise NASCAR, what era? again 50's/60's is best otherwise you end up with a grid half full of jelly moulds.