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The port most often used is the one on the oil filter boss, just above the filter/block joint.

oil pressure 2.jpg

Depending on the year of your block, you may also have a second port located on the block behind the distributor, just below the driver's side intake to block joint. Some guys running a stick find that the clutch bellcrank requires some creative plumbing adapters to use the one on the filter boss.

oil pressure.jpg