well I know it goes in the boot

but where?!

I have what I believe to be a 405 original fitment CD changer with brackets but I cant figure out where its meant to be fitted.

It attaches to the 'roof' of the boot, right in the middle. Dont think i have a photo, surely somebody on here does!

Yep, my old MKII had a bracket and pre-drilled holes in the underside of the parcel shelf and it hung there, not a bad set up and out of the way, cept if you were trying to cram something in right up the back!