Hi,
I'm sorry I don't know what you mean with struts? Do you mean the gas springs or the u profile on the piston rod? To find out the right length, force, angle and place of mounting the gas springs I had to buy several springs till I was satisfied. You have to find out by yourself which one fits good for case. If you have the right spring you probably first have to change the plastic joints on the ends to metal joints. Then you measure the diameter of the piston rod and take a u-profile which is slightly wider than the rod. Then you narrow the profile at the ends with pliers so that the profile is clamping on the rod when you push it on.
I hope you can understand it and I could answer your questions.
Greetings Henry