Greg & Stuart,
My Suburban went through a total restoration. In almost all cases, as Stuart describes above, installing screws into the sheet metal established a good ground. A continuity-check assured the grounding. I then unscrewed each screw and applied Kopr Shield to the screw and dabbed a little into the hole in the sheet metal (using a fine-tipped brush).
So far, I have only had problems with one grounding inside the "case" of one of the side-mounted accessory dual-rear tail/stop/signal lamps.
I also use Kopr Shield (a conductive anti-corrosion paste) on my battery posts and on all my body/frame grounding straps (00 gauge). My 6v starter turns very nicely.
By the way, a ground strap from the head (one of the coil-bracket bolts works nicely) to the firewall (one of the fender-brace bolts works nicely) assures an excellent grounding to the cab sheet-metal. I dimly recall that this is specifically required as apart of the installation instructions that came with the 1954 radio.
Tim
