Here are a couple of threads you may find useful info in.
Instrument cluster, gauge type
http://67-72chevytrucks.com/vboard/s...d.php?t=709847
fuse panel
http://67-72chevytrucks.com/vboard/s...d.php?t=741245
Which fuse are you checking? I had trouble testing for voltage through the rust, but if you stab the voltmeter or tester into the fuse end cap and fuse holder you should get a reading. The fuse outlined in purple in the picture below is the one that should have power in the key on position.
Check for voltage on the pink wire at the instrument cluster. With key in on position you should be getting power on that wire.
Are your instrument cluster lights working? How about the turn signal lights on the instrument cluster? Does the brake light come on during start?
Is your instrument cluster plug have the wire colors in the correct spots on the connector? I ask because the non-gauge cluster has different wiring at that plug.