Hi Guy,
My Leda struts are M14 x 1.5mm. I have a die if you need it to clean up the threads.
Ref the springs.. I recently got a new set made in Sheffield £80 for the pair plus VAT and carriage. (300lb spring rate)
The company was "Springcoil"
I know you may not want to do this, but your springs may be a bit tired.
I have an original set of springs from Gerry that you can have, but they're VERY hard.
Cheers
Andrew