Contacted Sig C/S and was told that the .357 Slide isn't compatible with a 9mm barrel, so to do what I want to do, I'd have to buy a whole new caliber exchange kit.
As an aside to my last post on the .357 Sig. The Gun Writer's are trying to kill the .40 S&W by now saying the "the .40 S&W is dead, the nine can do it better". One such writer that writes for Firearms News is one of those guys. Well I have been a subscriber to that publication since it was called Shotgun News and since it's inception. I called and complained to no avail as I was treated more like I was more a Liberal than a Conservative gun owner. I have been told in the past that ALL that publisher is interested in is $$$$$$$. I canceled my Subscription after what? "50 years"?
The glocks all you need is a conversion barrel from Lonewolf and a mag, although I’ve used the 40 / .357 mags without any issues at the range.
The only full slide I had to purchase was an Advantage Arms slide ($250ish) that loves cheap Remington Golden bullets, the G23/G27 platform is really versatile.