slant six oil pressure sender is where?

Melling MV66HV. Port is plugged, remove it and it looks like it may require a 3/8-18 NPT adapter for the oil pressure sender, but NPT is always much larger than it sounds so it may in fact be a straight 3/8 NPT plug. They used 1/8 NPT senders also over the years @slantsixdan
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