I've never been very keen on the way of setting Lucas MCR2 and similar voltage regulators by using the bike's engine to set the cutout and field voltage regulation. I was browsing ebay and came across this:
https://www.ebay.co.uk/itm/Adjustable-AC-DC-Power-Supply-Adapter-Charger-Variable-Voltage-3V-12V-Universal/362934886316?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649It made me think that maybe I could use this to bench test and calibrate the regulator I'd had in a box of bits as I had no idea whether it was working or correctly calibrated. So I bought one and after checking the mechanical aspects of the regulator I used the voltage supply connected across the dynamo and earth connectors to set the electrical side. The voltage control is a bit coarse but I was able to successfully get the cutout (well cutin really) operating at the required 6.5 volts approximately, and the voltage regulator operating at around 8 volts.
I then put it on the bike and it works perfectly.
May be useful to someone else?