Yeah, from what I understand, the closer you are to 10-1/4" the better off you are.
Having said that, a wolff spring might be the right length, but it still might be too stiff. IDK. I just know from people on here that some wolff springs have been known to be too stiff. I don't know if I've ever experienced it myself. But with these older carbines, your best bet is to stick with USGI or something comparable. Orion7 has a good rep with the milsurp guys. From what I can tell.
Oh, one more thing, I bought my springs from fulton when I first got my carbine and they were too short. I didn't realize at the time and just figured they were gtg. But I've since learned they might do this regularly. And my carbines haven't run properly yet. I have to get them out since I replaced the springs.