Question on converting standard 71 cluster to ralley?

Hey Guys,

I am working on a 71 Demon with my son, and it has a standard gauge cluster in it. I have a 71 ralley dash and was wondering what was involved in switching it over? Do I need a new dash harness, or can the standard one be used? Someone told the me dash frame is different. Does the old one have to be cut to accept the ralley dash? I would appreciate any advice or tips on the conversion.

Thanks!
Randy