IIRC, the voltage stabilizer is on the back of the dash under the radio on the passenger side. It might also be near the dash rheostat, I'm not sure. It could be bolted to the fiberglass in front of the dash on the passenger side, but I don't think so.
The parts manual isn't clear (maybe you found that out already!). The closest thing I found to a "voltage stabilizer" was "instrument stabilizer". In the MD section of the parts manual (Electrical Instruments) (see picture below), it shows the instrument stabilizer (#30)in what looks like the bottom area of the dash (that's covered by the console cover). Of course, the picture is not necessarily meant to locate anything. But then in the description block, there are several #30s (see second picture) that are in no way related!
In any event, if you're trying to find it or a place for it, either of those places would be highly likely.
Does that make any sense at all?