Assuming your '84 Westy has the same A/C as mine, it was put in at the port of entry.   Mine says Ft Worth Texas.
The expansion valve is of very common manufacture of the period and probably has an orifice,seals most suitable for R12.    It is located on the rt side of the evaporator coil in the rear ceiling mounted unit and is where the hoses are connected and is probably covered in something that resembles modelling clay.
Stuff like this is becoming insreasingly difficult to get as these days generic components are set up for R134a.
If your system has been kept dry it will probably work ok.
Replace all the O-ring seals with the newer green kind even if you intend to use R12,( I can usually find them at Pep-boys) and replace the receiver/dryer mounted in the drivers door wheel well.
Also if you want to upgrade to R134a you will need to use a different type of hose, with a barrier lining as the molecules of R134a may bleed out through the older hoses.   There are of course many issues to deal with if you convert although many claim that the simple Castrol kits work fine.   I personally prefer to stay with R12 for the moment,as I am certified to get the pricey stuff.
Good luck
Steve