Hey wilkid, don't ask why I measured for this, but here are some measurements of the radio bay that I wrote down at one point:
width: 202mm
height: 86mm
face width: 206mm
face height: 91mm
Sorry about it being metric, but you can convert easily.
There's a metal tab sticking up behind where the radio goes - anyone know what it's purpose is? I think it can be safely bent back - doesn't really seem to serve a purpose. With it in it's current position I'd estimate you've got 150mm of depth, and if you removed it you could go a lot deeper.
Speaking of which (and not to hijack the thread, but), I'm looking for a flush mounting kit for my Aiwa CDC-X437 (177mm wide x 50mm tall) that has a pocket underneath it, to put in my Fiero. I could use the pocket for CDs or papers, and I hate how my radio sticks out - would make it look more stock.
Hope it helps!