I believe you will have trouble finding/matching a sender to the gauge. Then there is the 12V issue...... and don't know if a GMC gauge matches/fits a Chevy cluster.
My suggested options: (headache prevention)
1. Buy a capillary gauge.
2. Buy a 12V electrical gauge and sender set.
It is possible you may find "original" parts here on Stovebolt or Ebay and etc.
Your 6V gauge would need a voltage reducer.
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