You don't need the small venturi to control a .40LA, so just get the bigger one. It'll be fine. You might want to try a Bruline air filter, tho. Get both fine and course filters.
I have no fondness for the OS needle valve assembly, having used them, ST's, ST Clones, K&B's and Nelson/Randy Aero, in recent history. I'd rate the Nelson/Randy NV setup to be #1 by a bunch.
Mufflers: The stock one works well if you can stand the weight. If not, a Randy Aero, Big Art or Scott Dinger tube muffler would work very well. The lightest and cheapest is the RSM Tongue Muffler, but I prefer a tube muffler for the quietude. You probably will also, and it may help your flying, leaving you more relaxed and able to concentrate better. Just $.02 worth.
Steve