I have been down this road with Ian John of Caerbont. Your 8N 16 transmitter is 0 to 160psig range (or in Caerbont's books 0 to 10 barg , not quite an accurate conversion but these bits of kit hark back to early 19th century in terms of build quality and accuracy, i pulled one to bits to have a look.
According to Ian we should use a 8N 10, which is 0 to 7 barg or 100psig (roughly!) and not the one that Morgan specifies, 8N 16. When i discussed accuracy with Ian he was non committal, stating that it was indication only. When i pulled a suspect transmitter to pieces i could see why!
I have installed a 8N 10 to match my standard Morgan gauge set up and at cold the oil pressure indicated can be as high as 6.5 barg according to the gauge.
The outcome as far as i was concerned was not to take the gauge too seriously, as Ian says its an "indication"
The resistance range at the input (i.e. transmitter resistance) that the 0 to 7barg range gauge operates over is 10 to 180 ohms = 0 to 105psig (or 7barg).
One idiosyncracy of the transmitter seems to be a drop in resistance and thus oil pressure reading when the engine is fully warmed up and running at around normal cruising speed 2.5 to 3k rpm. If you momentarily reduce to tickover the reading recovers. I've carried out a couple of checks against a direct reading bourden tube type gauge and verified that the issue is in the transmitter.
All makes the gauge readings a bit disconcerting if you take them seriously!!
