You are very welcome Stephen.
I assume you have the schematic for your Viking Mobile and if so the footnotes on it show the three connections that have to be changed in order to use a dynamic microphone. The default setup is for a carbon mic so if it is original or restored to original then it will be set up for the carbon microphone.
Your Mobile may also have the PTT relay added, if not it is a fairly simple addition if you want to use PTT.
The Geloso VFOs are very nice assemblies. I have a Geloso AM/CW transmitter receiver pair along with two iterations of their SSB oriented transmitters and receivers and a homebrew CW transmitter that someone built around a Geloso VFO. The stability seems quite good with the Geloso VFO.
There probably aren't many Viking Mobile owners in Australia so you are in an elite group
For several years one kept showing up at local hamfests wrapped in plastic wrap and priced at $400. I waited until I found a much better price on one.