How to add on gauges??

Installing the 3 gauge aftermarket set won't be any problem. They all, afaik, come with instructions to follow. Doing what you are doing, you might consider deleting the amp gauge though. I've just learned about this myself. http://www.madelectrical.com/electricaltech/amp-gauges.shtml

I wonder if anyone has a volt gauge/meter that replaces the amp gauge in the dash for '72 Dusters. Someone pass it along please if there are.
C