Just to be clear you have the three hole cluster with the center warning lamps right?
If so adding a gauge cluster or a gauge and tach cluster is pretty straight forward.
Once you have a cluster the wire harness connector/plug needs to be repinned to match the gauge cluster correctly.
A gauge temp sender needs to replace the engine's thermal switch.
Then the oil pressure hard line running from the engine to the cluster is added.
If you are adding a tach it has a seperate harness as well.
Tbone1964 reconditions clusters but shoulld be able to fix you up with a tested ready to go stock cluster assembly.
http://67-72chevytrucks.com/vboard/s...d.php?t=604141
Or you can just hang some add on gauges that are electric or mechanical.