For next time i'm in there... how did you split the heater box from the evaporator?
In terms of top of heater off from bottom to remove the bit with blend motors and core leaving the exposed aircon end - there is one screw in the top (on mine, the upper left of the heater inside the top duct facing towards the bonnet). After the middle metal frame is out of the way and the four big floor bolts for the main dash frame slackened the heater can be pulled up and out leaving the aircon end in the car.
Rest of car without heater (1) -
It might be the screwhole visible in the plastic over the heat exchanger but not sure tbh. There is also a new screw there now, and the old one is somewhere in the heater. Managed to nearly forget it and then drop it in after the whole lot had been squeezed and wriggled back into place. Vac plus garden hose & magnets on sticks haven't found it, so it's still in there. Also - on mine the airduct for the screen vents under the dash is separate from the dash itself (which has come unstuck over the years anyway - delaminated, need to fix it when I finally do the blend motors after the winter) and might/might not conceal the relevant air outlet. Needs to come off anyway whichever.
(1) - Somewhere I had a photo of the heater box leaking all over the office floor, but I can't find it right now.
EDIT - Sorry Gilbert, It's not that I didn't read your post but I think I was typing mine slowly so yours popped up between starting and finishing. Yes, it's exactly that - one screw.
Btw: Leolito, it's the middle bit that (really takes a bit of pulling and the 4 big main floor bolts loosened off) has to come out, on mine it's the alloy coloured not Oxford blue bits.