As it turns out my memory was accurate for once and the reg/rect output is 15.6v at the battery more or less throughout the rev range, rather than 14.5v as recommended here -
"Re: Charging issues
ď„Ş
AWJD » 05 Aug 2017 1415
If you disconnect the 3 wires from the alternator, you should get a low resistance reading from each pair of wires. This would normally indicate that the alternator coils are basically sound. Unfortunately, the rectifier diode test only means that that part of the RR is ok - it doesn't mean the regulator output part is ok, unfortunately. If the alternator appears to be ok then the overall test for the RR is whether you get a voltage output of ~14.5V from the RR red/black wires when the engine is running. If not, it's likely the regulator has failed."
-so I guess I'll try the old Kwack one which Brickboy gave me.