Good report.
Sorry to hear you're experiencing problems shooting with the light attached. As you probably know, alot of other folks have that issue.
Glad to hear it runs good in .40 though without it.
If having the light on is imperative for you in the defensive role, sounds like it may in fact be best to run it in 9mm then.
Glad to hear it runs well that way though. As it's an aftermarket barrel, I'd suggest running at least another 300 rnds through to absolutely confirm reliability. And a fair amount of a chosen defensive load. I know that gets pricey, but being an aftermarket barrel, you want to know it's good to go.
I didn't fully trust my G23 9mm conversion until I'd put about 800 rounds through it with no malfunctions. Just wanted to be sure.
As far as parts being interchanged for reliability, all I've done is the Extractor. Runs very well with the .40 Ejector in the Trigger Housing.
If you wanted to go "all out", I'd say the Extractor change and a Trigger Housing w/ 9mm Ejector in place would be all that's needed. It would be truly converted at that point.
Obviously the Trigger Housings for 9mm and .40 are 100% identical................I just speak of changing it due to the fact that the Ejector is rather firmly pressed into it. And you want that part to stay "tight", so it's a much better option to switch the whole Trigger Housing, rather than prying the Ejectors themselves in and out.