Have a 35 I converted to 9mm with a Lone Wolf barrel. Shot 9mm through it with both .40 and 9mm mags, no change to extractor or guide rod, shoots 100%. Put a lighter recoil spring in for competition shooting, but not for reliability.
I converted my 3rd Gen Glock 31 (full size .357 sig), to a Glock 17. I swapped in a 9mm ejector, Glock 17 slide and recoil spring, and Glock17 mags. Works like a charm. Some people say that you can use the .40/.357 ejector with the 9mm configuration, but it's an inexpensive part, so why not do it right?