But I have to say, you're a star!
. It was a fiddlier job than anticipated, bearing in mind access wasn't great, but with your excellent instructions I was much better prepared. The first time I thought I had mounted the diaphragm on the spindle, it was taking a lot of force to get it through the hole, and then realised I'd actually made a new hole in the wrong part of the diaphragm! - luckily the kit had exactly the same diaphragm for the other side, so I was able to use that.
Because it had been so fiddly to get the spring, metal plate and diaphragm on and in the right position, I cheated a bit and put a bit of superglue to hold the metal plate to the diaphragm and the external metal plate, which made it a lot easier.
The hardest bit was getting the metal ring and cover on. I had to give up and get the garage boss (who was ultimately responsible for the problem) who has small and muscular Ecuadorian hands to get it on, and he spent about 15 minutes at least before he did it.
It's possible to see the small splits on the old diaphragm presumably caused by the engine being dragged past.
The front ride height is a little low, and not self-levelling in the same way the back does but this is probably best dealt with on a separate thread.
Anyway the main thing is I have a usable car for the first time in a long while. Thanks to everyone, and especially Citronut, for your help.