The slide rod unscrews, if I remember right, and then you can put a spring on. If it turns out to be a press fit, then push it out and replace it with a 4/40 (or 2/56) rod end so that no threads show and use nuts to hold it if necessary. Use a small wheel collar on the top. I've made a few of these and they work ok.

Yes, the slide linkage twists, the spring will give it more friction against twisting. It is a problem but if you keep the linkage high on the slider and the pushrod arm straight on it will minimize the problem. You might not want to use a nylon clevis as the strut gets some good shock loads which can shear the nylon pin. I use a steel kwik link. A Z bend can hang up if the top of the Z is too long.

I've seen standoffs that attach to the springair unit that keep everything aligned but they were all homemade. Pushrod alignment is important and needs to be straight on to the linkage.

Dubro is now selling a long flange nylon link that might work better as a slider with a kwik link if the hole is drilled in the right place.