Just a short update.
On the weekend I removed the throttle mechanism which mounts on the firewall, intending to clean it up. Once I started, it looked OK, but I decided it would benefit from a coat of paint. I painted the main mechanism VHT Cast Iron, and the vacuum unit in aluminium. It looks much nicer now. Sometimes it is the small details which make the difference.
When I travelled to the US a couple of weeks ago, I carried the heater valve in my luggage. Once I arrived I posted to Old Air Products in Fort Worth, Texas for a rebuild. The valve arrived back today, and I have to say the quality of the work is excellent. It basically looks like a new valve.
The price from Old Air Products (US$86.50 plus US$47 shipping) was significantly cheaper than most, however classic car heating and cooling is what they specialize in. Looks like it was a good decision to go with them.
I also dropped my radiator and heater core off at Dandenong Radiators on Monday to be flushed, cleaned and pressure tested. Once I get them back I can start re-assembling the HVAC unit. There not many radiator repairers around any more as newer cars are always a replace and throw away process.