Hi chaps.
Firstly, thanks for the replies and the help.
As to the moving of the head unit, I got a big kitchen pallet knife (sorry mum) down the side of the unit, to feel for obstructions. Incredibly, in spite of the Halfords chap bending the springy clips inward permanently, it was still catching. After lots of pursuasion, two of us, one pulling, then other wiggling/sliding various slim tools down to push it inward. Pushing back in, wiggling, pulling out etc. I had a change of tack. As you will be aware, the head unit is held in by metal, the actual centre of the dash is held in by plastic, so clearly serious force would only snap/break the
wood plastic trim, and not withraw the radio, so further brute force was only going to end badly. A hacksaw blade held by mole grips, to take off whatever was causing the obstruction with a gentle sawing action in and out of the dash brought the head unit out in about 2 mins

The casualty is one single clip on the left, which I can replace at my leisure, I'm guessing these are the same on any 90s Vx radio (
if I choose to leave these on, these are now removed for easy install/removal purposes) a single torx screw holds these on, for future reference.
Cannot understand how this was stuck out so much, but at least it's out.
Found my SC804 radio instructions, too. So I know how to programme/add the code/de-code the little bleeder, too, now!
Next step, put original HU in, and start looking at these contacts, then. Will report back when I know more. Thanks again boys.
