Thanks to Rob I now have most of the parts I need for my prototype Impreza loom adaptor.
This will be built over the next week or so.
I have had an idea regarding a production version... It also has potential applications in other areas, provided the costs come out OK.
We take a VEMS case extrusion and chop it into 3 (or 4) pieces so that we have 3 smaller cases. Take some standard end plates, some PCB mount EC connectors that mate with the VEMS connectors and then the Subaru ECU connector. Make a PCB where these all fit, containing the transient diode and resistor packs and you have a very neat robust P&P solution...