As I was unable to find a NOS clutch spring for my pals M20 that I'm repairing I decided to carry out the mod. to the clutch nut as detailed in the M20 standards book...
My only deviation from the suggested format was to use 4mm screws/nuts instead of the 3BA screws/nuts shown on the sketch that accompanies the instructions..
It was surprising how well this works to adjust and 'level' the lift of the clutch pressure plate..The only real drawback is that the pressure plate has to be fitted to test the lift, then removed to make adjustments and then refitted again to test the results...This procedure then has to be repeated as needed until the desired results are achieved...
So, it's a bit of a patience test...
Care must also be taken to make the screws the right length, so as not to contact the inner face of the pressure plate when it is refitted (That would prevent it seating correctly)...
Anyway, the end result is adjustable, rather than non adjustable, clutch lift and an extension to the operating life of a clutch spring that has 'settled' after extended use with the ends out of square....Ian 
email (option): ian@wright52.plus.com
This is the page from the standards book...Note that if the 'dodge' of leaving out one fibre and one steel clutch plate to allow more space in the clutch basket is employed, there will then be a clearance problem between the back of the clutch pressure plate and the heads of the screws...
To overcome this I made a spacer equivalent to the thickness of the two plates that fits under the clutch pressure plate...This is basically a plate with six holes that conforms to the dimensions of the flat part of the pressure plate...Ian
email (option): ian@wright52.plus.com