I have a text file of notes I made when I did a total strip-down on a 4a. If you PM me your email address I could send it. I took lots of pictures, and I'm slowly combining them with the text to make an html page of the job, but I am not very far down the road yet!
If you are aiming to replace the springs (there are 3) in the curtain spring-spindle let us know how you get on. I stripped the spindle as far as I could because it needed cleaning due to corrosion, but without removing the springs. Due to the way they are attached to the spindle I decided that it would be next to impossible to re-fit them successfully.
Anyway, worth a try if you have a broken one, so best of luck!
Steve.