Messing with the distributor is opening Pandora's box. The vac. advance is
set for a standard engine. If you improve on that you will need to change
the vac. advance (characteristics) to suit (good luck!!)
Remember that Vizard is working on performance motors, the electronic
ignition will improve spark performance and exact timing. That allows for
greater precision all round, and improves performance. - i.e. so both your
statements are correct - it's stock and it's better!
I suggest you use the standard centrifugal weights as these work at rather
low speeds and are standard throughout the range on
cars/engines. Distributor efficiency does itself not impact the advance
itself, but could require and change in characteristics (5.12.6) from
standard. Again, good luck in sorting out whether more or less advance is
required more or less quickly.
I would remind you that the Mini Cooper solution to this problem was to fit
a distributor without vac. advance, but again, its engine characteristics
were different (?). There was a Mini Cooper spec advance, it would be a
good place to start if the standard unit is a no go.
For a treatise on the subject: www.wolseley.asn.au/flying/fw1/tuning.html
Let us know how you make out!!