Manosound pointed out to me this thread and suggested I may be able to comment usefully.
So here goes.
Guy, your very best bet would be to purchase a DVR2 directly from us a Dynamo Regulators Ltd.
Seriously from the connections on the Cargo regulator you have (not heard this name before) it should work with your dynamo with a wiring modification to the field winding. It is for so called series field connected dynamos, not shunt as standard for Lucas. You would need to move both ends of the field winding in your Lucas machine. The one from F terminal to go to the output D and brush, the end going to the body is then moved to the F terminal.
What puzzles me as well is that the regulated output, often labelled 51 or 30 seems to be missing. Perhaps you could post some photos to clarify.
I think is advisable to fit a fuse.
No insights into the Nissan regulator but agree that it is probably for an alternator.
Cheers
Mike