I'm still working it all out on my own, and I'm sorry if this doesn't quite belong in this thread.
However, here's what I've figured out so far.
I've got an EG33 swapped impreza, and it's now got a USB cable in the glovebox that will give me data, but I don't have all the settings right in the hex to be able to interpolate that data.
You can do some reading here: http://www.alcyone.org.uk/ssm/ports.html
Most of my info is going to be for the SVX, as that's what I've been working with, but would apply to most subarus with an SSM port as well.
Basically SSM uses a TTL signal, which you can convert to a USB signal, and then use software like VWRX or EvoScan or Rom Raider to read and interpret. (http://www.alcyone.org.uk/ssm/software.html
Furthermore, the VWRX software does have support for 92 subaru NA, which I can only assume to be the legacy (Impreza didn't come out until 93).
So, it may take some playing around and learning hex, but it's doable.
Or you could make friends with the dealership, because they'll probably have one that hasn't been used in years sitting around the shop that would plug right in.
(also, damn I haven't been on in a while, Mods with member numbers higher than myself?! Makes me feel old.)