OK, so you are Pos earth already, and it was (over)charging, so let's assume polarity must be correct and that the field coil is wired 'per Lucas' and correctly for a DVR2. Let's also assume for the moment that the dynamo is working, as it was chucking out volts, and presumably supporting 'loads' as the ammeter was showing a large charge rate. And dare we assume too that there isn't an unwanted connection at the dyn between F and D, which would prevent regulation from ever happening?
I wonder what the battery voltage is, right now? Has it dropped back to 'sensible' - as in 6.something volts - or is it still showing an unusually high voltage? It shouldn't, but if it does your DVR might not kick in because it isn't designed to support a battery with a higher-than-it-should-be voltage.
As is often said, with a correctly charged battery you'll see very little on an ammeter by way of charge because it doesn't need anything more than the lightest trickle - but what happens if a battery is showing a voltage above the 'system voltage' when the engine's running (which is 7.2v on a 6v system) is territory rarely-visited I think! A single voltaic cell, fully charged, will show 2.2v; a 6v battery has three cells, so a reading of 6.6v is 'fully charged'. Anything more than a small margin above that is abnormal. Regulation is set typically at that 7.2v level to ensure the maintenance and gentle charging of a fully-charged battery.
What I'd do next, if you can bear it, is hook up one of your DVR2s again, to the dynamo and to a good earth - ie green yellow and red leads connected.
I wouldn't connect the combined brown and white doubled-up output wires to the ammeter/switch just yet.
Start the engine, and put your multimeter, on the volts scale, between brown & white and any good earth. If the dyn & regulator are working, you'll see volts coming out as the engine revs, and it should settle at around 7 to 7.5v. It will be spiky, especially if using a digital meter, but it will show whether there's activity well enough.
The battery does not have to be in circuit for these particular regulators to work.
If there is no output, then there is a problem with the dynamo or the wiring between it and the known-working regulator.
If there IS output, then we need to move upstream:
Hook the brown and white wire into its allotted spot at switch / ammeter, but leave the battery disconnected, and run the engine again.
Do the lights now come on above tickover, and go off again at v low rpm? If so, good, that's what they should do. And if they don't blow with a handful of revs, or go far brighter than they ought, then you're regulating OK. They'll flicker a bit at lower revs, but will look steady as revs rise. If all the bulbs do go pop with a few revs, then it's not regulating . . .
And now what happens if you connect the battery up again . . .?? In a well-ordered world, nothing bad. You'll see a small charge on the ammeter and the battery should show a voltage that is slightly higher with the engine running at revs than with the engine stopped or at tickover (and never anywhere near 9v!). . . In an evil world, who knows? You'll find out, if you get as far as having a system that works until you hook up the battery! In which case there's a problem between ammeter and battery, at the battery wiring, or with the battery itself.
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