On my 6v Suburban, I have ground straps from the frame to the clutch housing on both sides of the engine. Also, a ground strap from the head to the firewall (GM spec for radio).
And, just to be safe, I run the 00 ground cable from the negative terminal on the battery directly to a starter mounting bolt (instead for the strap/cable from bettery frame.
My only weak grounds are for some lamps/bulbs, where a screw into sheet metal provides the ground (I failed to expose metal through the epoxy/urethane layers in sheet metal/etc).
