G'Day UncleD.
There are several factors worth considering, the major one for most people is cost. Replacing the magneto as a carrier for the system adds considerably to the outlay.
Provided the magneto is in reasonable order, my choice is Thorspark, which retains the magneto and existing ATD, simply substituting the contact breaker points plate for the electronic trigger. This fits entirely inside the end cap. This output is fed to a twin lead coil, firing both plugs at the same time, avoiding the imbalance you have with the pesky cam ring. It is available in either 6volt and 12volt versions, easily fitted and can be removed without any alteration to the magneto. For comparison, in the UK today it is priced at £150, plus a quoted £17.50 for postage outside Europe. They may have agents in OZ.
The exiting Tacho set up will work as it is driven as before, theoretically the extra drag on an ATD may alter the timing at low speeds, until full advance is achieved, which is why standard set up was magneto drive, with solid cam wheel and manual advance.
Pazon and Boyer systems are widely available for later points/coil type systems, as on your A65, but when it comes to magneto systems these types generally require a new housing, which adds to the cost. However, these systems have electronic advance and a solid drive gear which is easily adapted to drive the Tacho gearbox.
If you win the Lottery, "Lucas" now market an electronic look alike magneto, as a further possible choice.
Be interesting to see what other Fellow Sufferers recommend.
Keep Spannering
Swarfy.
Additional.. Add Tri-Spark to possible choices.. Thanks Pete.
