Well, that is much more promising news.
When you say you have swapped to 15mm springs does that mean 15mm lowering items? Were they in the motor car when you bought it? I ask because (if you don't mind me saying so) the motor car still looks a bit low at the rear. IMHO (and I know, that isn't important) it would do the motor car no harm to raise the back by at least another inch.
I don't know anything about adjustable Panhard rods, although it is obvious what they do. If you measure how far the OSR tyre sticks out and how far is the overhang on the NSR side that will give you your leeway. It sounds like the gap would have to be huge on the NSR to have enough spare room to move the OSR sufficiently, but you will be able to work that out much better from where you are standing :-).
It is really sensible to have spoken to other people about this conversion, well done. I only know what I've read (mostly American stories on Turbobricks); many owners seem to report rubbing problems with wide 18" wheels (not the same as your wheels though), although often at the front, where the solution is to restrict the steering with some blocks. This seems a pity to restrict the turning circle of a 240 as that is one of its strong suits, but may be a necessary price for the look. Americans resort to flaring the wheel arches at the drop of a hat to solve rubbing problems. It doesn't look like it would be all that difficult, but it would be more difficult to find a body shop with the experience to do it here in the UK. I'm not sure what you mean by trimming the arch a bit though JJ, IMHO if any metal needs removing then it needs to be done properly and some sort of flare added to replace what comes off.
I think you have come to the right conclusion about the tyres, this is going to be a close run thing and 205 is the widest tread that might fit. You already know my feeling on stretching tyres, but I'm much more conservative than are you JJ. Unfortunately 205/35 isn't such a common size, so what is available is a tad more expensive. At the cheaper end of the market a set might be had for £400 (fitted), which isn't so much in the context of the whole project.
This has suddenly gone from a 'tidying up an old motor car' project to one breaking new ground (for our very conservative 200 series forum) with lots of interesting technical and aesthetic challenges. We are enjoying reading about your progress JJ - keep sending the words and pictures.
:-)
Alan
PS. These are the 7.5x17 wheels I bought for GAM (my 1963 Amazon):
... I'm pretty sure they would have fitted with some 205 section tyres but I knew they were wrong (much too ZZ Top) straight away, and that view was corroborated by the voice of the body of the kirk in the 120 section of this excellent forum. I was happy to put my hand up and admit I'd made a mistake instantly; no harm was done as I'd bought them very cheaply and sold them on at a profit the next week :-).