OK - some more updates on this... I've been working through it slowly evenings and weekends since and it's pretty much back together now...
Stripping everything down isn't too hard, it's just time consuming. The Lotus service notes say that the rad has to come out as a pack - main rad, chargecooler rad and AC condensor, but it is possible, if awkward to split them apart in the car and just get the main rad out.
Putting it back together without splitting the rad pack is much, much more awkward. If there's a next time, I'd probably take all three out. But it is possible.
Some of the rad hoses / chargecooler hoses were a little crusty and starting to weep, so these got resealed and some extra clips on them to hopefully prevent any future issues. I would probably recommend inspecting the hoses behind the arch liners if possible as part of general maintenance - for the sake of an hour or so it's better than having a major leak.
Putting the bumper / clam back on is more fiddly and time consuming than difficult, it just takes a while to get everything to line up nicely, make sure the panel gaps look OK. Likewise with the headlights - the mountings and adjustments are a nasty nasty design and it's fiddly to get them aligned in three dimensions and sat in the recess nicely.