Hi Tony,
That is interesting about molecule size & leakage. I hadn't heard that before. I would expect that an R12 TX Valve should work o.k. on R134a, because the pressure/temperature relationship is quite similar.
Just a point on your advice about changing out the components & then having a licensed Technician do evacuation & charging. That is good advice. It is only mechanical work.
My point is to suggest that you don't fit the new filter drier. Leave the old one in, & for the technician to fit the new one. The "drier" part is a dessicant, which will absorb moisture from the air, which will be in the tubing.
Another point is to be scrupulously clean. Dirt & moisture are killers for refrigeration systems.
 

Denso 047500-1730 fits my 1990 R12 evaporator
Purchased from Autofrost.com.au
Update 12/02/2016: it's not the right one, it's backwards. See my posts below
Update 13/02/2016: ok it is the right one, I had accidentally purchased the wrong evaporator which is why it was backwards (I think the US ones are backwards maybe?) 
 

 
 
 
 

 
 

 

mr2y
I am presently eating my own words. When I tried to bolt everything together with the 47500-1730 it is backwards. I'm guessing Taragos have the TX valve on the other side of the evaporator. Spoke to my local air conditioning guy he said the R12 ones work fine. So I think I'll go with Tony's solution, cause this valve isn't going to work.
 
Edit: ok it turns out it WAS the right one, but I had purchased the wrong evaporator, which seems to be backwards so I'm assuming because I bought it from the USA it's for US cars, not JDM.

Wish had seen this before I ordered my evaporator from the states
I have exactly the same issue :(
Any chance there will be a Tx valve available that can be installed the other way?

Please pm me his details, I am also looking to see if it is an option to cut the evaporator inlet and flip it 180 degrees and get it welded back
Might work out a lot cheaper than buying another one