Hi Andrew,
Thanks for your e-mail and the chat on the phone and sorry I hadn't seen this thread until now. I obviously feel some concern and responsibility having worked on your car with you.
I read back through my notes and remember we removed a damper on one side due to the two spring platforms being locked together. The spring went back on the same way around as removed and all was well, and the flat floor set up continued.
I have checked both build manuals (photos) I have here and compared it to a local Severners SV and sure enough the springs are the wrong way up, just as BIO and sparky suggest. Neither of my build manuals seem to mention which way up the springs should go, is this because they are already assembled as complete units in a kit?
The odd things for me is that it must have been like it from new so am surprised the orginal owner or Caterham didn't check this. I remember you saying the previous owner had set the suspension to be that low, although I can't see why he would change the springs over?
One of the things we rectified was the total ride height, in particular at the rear, which was far too low and only gave 4mm rake. It's maybe this change of height and so angle which has caused the spring to contact the metal panel, where there was previously just enough clearance or an unnoticeable amount of rubbing.
Having also looked on google for 'Caterham rear spring' I agree that most photos show the spring the wrong way up (the way it is fitted to your car).
A previous thread didn't raise any concerns about orientation - here
I think what you propose is correct; fit the springs the other way up and go for a drive and report back. Let me know if I can help in any way.
Cheers, Dave