Right, made some more progress on this on Bank Hol Monday.
While the ECU box was out, a quick wire brush down on some small areas of surface corrosion underneath it.

Rust treat

Spray with Dinitrol (Love the fact it's a non-metallic black car lol)

Refitted. Exciting, huh?
Trying to stop the bottom bayonet connector corroding again so I can get it apart in future, wrapped it amalgamating tape to protect it from salt spray.
De-rusted air intake pipe bracket

Also correctly re-shaped so the inlet hose nearest the rad isn't squashed any more
Front headlight had suffered from a bit of water ingress (turned out someone had had it apart before and not re-assembled correctly, squashing the seal) so took it apart in the hope it might just be deposits that would clean off with meths

Nope

But did at least get the glass nice and sparkly and it won't leak any more

The other side had always had this little sod in it, so it came apart too while I had the opportunity.
Back together and treated to a new set of indicator lenses because the originals were discoloured and covered in tiny surface cracks. Bargain at £9 each
These brackets from under the rad carry the bottom hydraulic pipe and large wiring loom. They were well rusty, this is after scraping and wire brushing. Stuck them in de-rusting solution intending them to only be there for a couple of days, forgot about them and then remembered a week later

Dark spots are massive pitting, not rust. Couple of coats of primer and Porka Alpine White (just because I had a load left over and what else am I going to use it for?)

The lary colour doesn't matter tbh because it'll be covered in a coat of black Dinitrol too. Refitted with all stainless bolts, 2 of which I had a massive fight with because of crap access (2 HOURS FOR 2 BOLTS!

) Mental note in future, if you remove brackets after the rad has been removed, ffs refit them before refitting the rad (and everything else)
Front end finally all back together,

And back on it's wheels
(hollow victory though, because as soon as I lowered the suspension again, it was back on blocks - still got some more wire brushing and undersealing I want to do before I move on to adjusting the suspension

)