Upon looking at the eBay ad for the parts, those were from the sale of our company to Remington Arms in 2014. It seems "someone" acquired this from the stash. Hmmm. Just a thought as Remington and whoever owns these parts now would probably not sell these things. So, moving on. . . . . with the horrible photo of the parts, if you look carefully at the slide it does appear to be one of the completed slide assemblies we sent them at that time to include: the firing pin, firing pin spring, firing pin retainer, extractor, extractor spring and pin. So the only things you need to add is the following items:
1. .380 Ejector and pin (Fatter than the one on the R9)
2. .380 Outer Recoil Spring (or a well used one from the R9 would work)
3. .380 Magazine
Change those parts out and you have the R380 AND an R9.
Now the real disclaimer: I don't know how this sort of swap works with the states that have the caliber listed on your license or any documents you have to legally own the gun. Being you now have the addition of the capability of using .380 ACP rounds in your 9mm pistol, there may be cause for you to investigate prior to doing such work to your legal R9 Pistol to keep things LEGAL.
. . . . and as the saying goes: "Just Saying"
So, can it be done relatively easy. . . . . . yes
Do I think it's a good idea. . . . . . . . . . . no
Good Luck with your decision.
Respectfully Yours,
Eric C. Rohrbaugh