14.35mm I reckon, although I have nothing more accurate than an adjustable spanner and a plastic ruler to measure things.

How about using that adjustable spanner and some feeler gauges to compare the diameters?
Adjust until it's a slip fit on the larger wire...

The van's springs' wire diameters are practically the same as the Special's, but the latter's have more windings (if that's the right expression).

In other news, got a replacement head for the one that I knackered a few weeks ago (sheared rocker bolt), courtesy of a v helpful fellow I2CVF'er. Fearing that I'd destroy this one as well, I took the short drive over to Peter Cross, who freed both bolts in about 3 seconds. Phew!

Lapped the valves and fitted new seals. Fitted the new head to the engine.

Finished off my new spring cans, painted them up and then fitted them to the chassis. Looking good.

Quick question: how many turns of the tie rods should you give, for a standard ground clearance?

there is no fixed ammount as the tie rods and the springs vary in size as does the can location.

as a rule of thumb with all 4 wheels off the ground the fronts so the eye is loose on the Knife edge and the rears so the eye just touches the contact edge.

OK - and thanks!

Can anyone recommend me particular padding strips that I should fit between the bottom of the body and the sub-frame, and where I can get it? I've heard that the stuff Citroen fitted trapped moisture - encouraging rot - so it would need to be some kind of closed-cell stuff, I guess.

It's called closed cell foam, but i can't believe it's actually completely closed.

Like this??

http://www.2cvcity.co.uk/chassis-foam-s ... -roll.html

or this, http://www.ecas2cvparts.co.uk/chassis-f ... p-405.html