ORIGINAL: BuzzBomber
Do both of those weights you list INCLUDE the muffler? I might be mistaken, but I seem to remember my OS .40LA being quite a bit heavier than 9.5oz, I seem to remember something more like 13~14oz. If that's the case, you won't have to change much around for balance.
I'm going by the weights posted on the OS website and Tower Hobbies website.