Can I put a CD player/radio unit from an Impreza or WRX in my '98 Legacy Outback? I've been looking at some on ebay and they all say "may fit other models" or "check with your dealer". My understanding is most subaru radio units are interchangeable, plug and play. Is that right?

Unless they are asking VERY little money for the unit, most people would be happier with an inexpensive after market stereo. They are almost as simple to install (they're still really easy though). For around $100ish, you can have a much better sounding radio.

To answer your question: Yes. I put a double din 6 disc changer stereo from an '02 WRX into my '95 legacy. It's a direct bolt in/plug in swap that can be had for under 150$ off of Nasioc.

AaahhhhAAA! so that means that Guage DIN faces for WRX will also fit!!!