Thanks for the replies so far guys. I really appreciate them. I've decided to go the Just Dashes route since I am building a show car and don't want to compromise. I have seen their work first hand at local car shows (in SoCal), and at their shop in Van Nuys, CA (I live only 30 minutes from them). I'm pretty sure I definitely need to give them a Non-A/C core, but don't know for sure it's necessary that I give them one that was originally a 3-speaker dash. Also, I don't know if I necessarily need to give them a '70 Challenger core, or if I can give them a later model and/or 'Cuda core that they can make into a '70 Challenger dash pad. I need to end up with a '70 Challenger, 3-Speaker, Non-A/C steel core, black dash pad. Any other advice is greatly appreciated. Thanks again.

FYI - I already made a post on E-body Parts Wanted looking for a core.