Thanks Scott. It's definitely not standard as it's a 60 tooth with 2 missing teeth design. The shop inspected the flywheel through the standard CPS mount hole, and it looks like there are no trigger teeth on the flywheel, so looks like that's also a non-standard component.
The car came with a Megasquirt, but it was not an MS-3 Pro as per the advert, and the wiring was a bird's nest. So a Haltech Nexus has now been fitted. It will be going onto a rolling road once these issues have been resolved. The weak signal comment was 4th hand, as the dyno guy had remoted in to help diagnose (so with live data feed), and it was his recommendation to replace the sensor.
Part of the issue is that there are no part numbers/marking on this sensor, and so I have no reference for the target air gap etc. I will ask the shop if they can experiment with this a little, but at Bay Area hourly rates, replacing the sensor with something that has a known spec might actually be more cost effective!