1983.

Yes, reading around the internet last night, I began to form that impression, but I can't seem to find anything definitive. Exiting the thermo vacuum valve on the block, there is a vacuum line that runs to a module behind the passenger-side headlamp, and then to the EGR. I've never known what that module is. There is a further line running from it into the cabin underneath the battery, which is perhaps a vent. I see on the diagrams of the vacuum system that there should be an electric switch-over valve between the thermo valve and the EGR, so I'm assuming this is it.

What exactly does this switch-over do? That's what I can't seem to find a clear answer to. I assume that whatever it does, it will require input from the VCV. So the reconfiguration would involve eliminating the 3/2 valve array on the valve cover, but keeping a line running from the VCV to the thermo-valve and then to the switchover?