If you are not welding to the actual cast hub, but are just welding on a spring perch and shortening the strut body to take a different insert then you can get a non destructive test (ndt) crack test. This is just a powder they put over the welds and shine a light on it. Only cost me 30 or 40 bux (over 10 years ago!) and got a piece of paper saying they were all good.
If you need to weld to cast, thats a no go. (here in NZ anyway) A lot of kits get you to weld to cast, so as long as its not one of them, you are likely good to go.
Also, should move this thread to the Cert questions thread.