won't affect the accuracy much adding length to the inner barrel. This has been proven quite a long time ago.
anything over 300mm, the difference is minimal, so it's not a bad idea keeping it 363(If you don't want to spend the extra bucks buying a longer one).
Adding a longer one will give you better FPS and slightly more range, however. But if you are already pushing the FPS limit with 363, it will go above limit with a little boost.
I always like having my inner barrel at least 20mm shorter than the outer barrel because this way dust/dirt is difficult to find it's way inside the inner barrel during the game, if you have inner barrel sticking out into the flash hider, the chance greatly increases.
Hope that helps.