Tricky to access the air intake plenum, with the recirculation flap out the way I can see a bit better but will struggle to get my hand in there to prep for primer.
Well here is one option, looks like you can drill out the spot welds and the entire top section comes off. But if I start down that road I can see it taking me 18 month to finish the job.
You could use a flexible shaft or a die grinder to grind off what you can reach and then cover the rest with Waxoil or something similar. It might be a bit of a bodge but the picture in your second post shows you how to do it properly.
When I saw your first post yesterday I thought the answer was to strip the car to a bare shell and send it for dipping but I new that was not the answer you wanted.
Hmmm...will need to ponder on this a while longer, bodge it now and do the big job when I retire (~ 5 years) or start it now.
This is the most concerning area, the rust has spread up from a rivet holding the trim clip just visible by the glass.
This is the first time I have been able to get in and see what it is like on the inside, looks like its just perforated through but not as bad as I thought. You can just see the back side of the pop rivet on the right.
Maybe one of the cheep usb endoscope cameras attached to a grit blasting tube ? Will fog up quick but lower pressure and a bit at a time. maybe have a vac at other end drawing out the dust (fog).