I am running a 71 up cluster in my 70 Challenger RT, not correct but unless it is something that really bothers you, use it. BTW my tach is very accurate, if yours isn't you can have them rebuilt (along with the rest of it as needed).
Met John Manush from 2K Inc. out of Iowa at the Nationals, does really nice work, will do only what you need and is a great guy to talk to. If you google the name you will see several "buyer beware" posts all from the same guy on multiple forums with a story of issues. Having read them (they are all the same), it appears that it was a clash of personalities, but then who knows. I do know I looked at his work personally and talked to him face to face and can say both were pleasant. That said, there are plenty of resto shops out there.