SPIM,
Gas struts are designed for a fixed distance. In other words each strut has a specific length and geometry that define where the 2 ball stud mounting brackets should be located. Hopefully, you "found" some that were the same length as the ones you are replacing, and/or the previous bal stud mounting brackets are still the originals. Also, Not all ball studs are the same size. So again, hopefully you "found" some that mate with the existing ball stud mounting brackets.
Gas struts are very susceptable to temperature, such that they work a whole lot better when its hot out, and not so good in cold. Gas struts do wear out, over time they leak the gas (nitrogen) inside of them through the seals. Once they wear out they have to be replaced because you can't refill them with more nitrogen.
Just in case you get them on, and they don't work as you might have expected - now, you have a couple of reasons for it.
There are different kinds of gas strut end fittings, but most just pop on with a quick hit as they are designed with a snap on feature. There are other kinds out there that require removal of a spring clip, to make it easier to put on.
Once on, the idea is to leave them on. These are not a prop rod, where you remove one end and put it in a stabilizing hole.
Good luck - I hope this helped.
Mike
bingo ! thanks man !