Hi Chris

As mentioned, until someone publishes a circuit, I am not familiar with the pre RP arrangement, and it is a pain to fathom from wiring diagrams.

At the risk of prolonging this, the direct links shown on the switch in Fig 1 of the article introduce confusion.
Whilst the article may have come out of A7CA mag, as far as I know it does not apply exactly to any Seven.

Digital meters do not work well in a car ignition environment, and they can get confused by erratic and noisy voltages.

Much depends on whether your system is operating as 3 or 2 brush.
Allowing for meter lead resistance, the resistance field terminal to 3rd brush (or earth if none) should indicate if wound for 12v or not. I measure at about 1.5 ohm for 2 pole models originally but others quote somewhat more.

From playing on the bench the field seems to tolerate considerable current without getting very hot; this may explain why many somewhat random 12v conversions survive. However in the car has a lot of other heat to contend with.

Location: Auckland, NZ