Hi Beezageezauk, I also think your dynamo is fine (maybe better than fine, as it can generate so much power!).
The discharge of 6amps with motor stopped and charge of 8 amps when engine running probably means the ammeter is wired correctly (but it's worth checking anyway). It might also be worth checking the various load/amp readings with a multi meter however, in case the lucas ammeter is not accurate.
That will probably still leave you with the problem that the ammeter is telling you the dynamo is overloaded, and with a 35 watt headlight bulb it almost certainly is being overloaded.
A 60 watt dynamo will help. 60 watts equates to 10 amps, but that's still not enough to supply the load you are seeing of around 16 amps, so the 60 watt dynamo will also be overloaded (this assumes the regulator maintains the same voltage for both dynamos).
Dropping the bulb wattages will obviously reduce the load.
Changing the battery to one that draws less charging current will reduce the load as well, a smaller battery will probably draw less current when charging (depending on type/brand etc), but of course will discharge quicker as well.
A regulator that limits the current drawn from the dynamo to circa 7 amps (40 watt dynamo) or 10 amps (60 watt dynamo) will be the best solution, but I do not know if those are available.
I've not yet run my bike, but have bought a DVR2 and a 6ah "AGM" battery that fits inside the OEM rubber case, I have both a 40 watt and 60 watt dynamo but will fit the 60 watt.
A few months ago, using multimeters, test bulbs and a drill to spin the dynamo I adjusted my mechanical regulator "on the bench" before deciding to go the DVR2 route. The main reason for going to the DVR2 was that I found that a "feature" of the mechanical regulator is to let the battery discharge several amps through the dynamo at tickover (when the dynamo is generating less than 6 volts),
To me discharging through the dynamo seemed a "waste" of valuable battery charge that I could not afford given the smaller battery I had fitted. I think the discharge occurs to avoid the regulator constantly switching the dynamo from "engine stopped mode" to "engine running mode" - with consequent wear/tear to the switch contacts, but I could be wrong.
The DVR2 claims not to "waste" battery charge at tickover like the mechanical one, but I have not tested it doesn't!