Standard Headunit

[choppa7]

I've had a look on the search feature for this answer but couldnt pin it down so I've had to ask, sorry if its a regular question.

The standard Panasonic HU in a 1987 e30, how is it removed?

I've had a look in the HU but the only clue I can find is a hole in between the volume and tuning knobs.

I've removed and installed a couple of HU's in my time so kind of know what to look for but I couldnt find any corresponsing holes anywhere, so is there just the one which holds the HU in or have I missed one (or 3)

Cheers!