Posts that stray from the original question often indicate how unknown the answers to these questions are. Differences exist within a model year & model. Bringing other years and models into the question doesn't help to clarify the question or answer. I know I am guilty of this also in my post above, but I was trying to point out the facts of the differences within Dodge in the '70 model year, after the Challengers got thrown into the post.

So ... does anybody have a b'cast sheet (or LA fender tag) for a '70 Coronet R/T, Super Bee or Charger R/T that shows: N42 N95 N97 ??

I think the original question was answered, N42 was an OPTION ($20.80 ) on '70 Coronet R/Ts.
It would be listed on the b'cast sheet or window sticker, and on a LA assembled car's fender tag.