under dash dilema

I was removing the dash pad on my 72 Dart the other day and noticed a lot of surface rust under there,like on the firewall.It doesnt look like deep rust ,,but like someone painted on a smooth layer of it..lol.I removed the heater air duct lines and glove box,,no radio , and removed the gauge cluster and have the heat controls just laying up in there ,,unbolted....My question is,,,whats the easiest way to tackle this problem,without taking everything out.Where there was sound insulation there was no rust ,,just the exposed metal has a layer of rust.,,,kinda wierd.Is there a product i can spray up in there ,,without having to worry about ohter componets being damaged.? How bout a light sandblasting...The whole interior is out pretty much,,so a mess from the media wouldnt be a problem...I dont think Im up for disasembling the whole under dash...