I'm resurrecting this one for fun. A friend and I were speculating on possible combinations and in my searching, a photo from this thread showed up in google. So I reminisced and re-read posts from years ago. One of mine caught my eye about people praising and condemning a full size, single stack nine if Glock ever brought one out. Sure enough, they came out with the G48 (close, it is the same length and height as a G19), and people are praising and hating it. More to the point however, is this pic.
I'll have to take a closer look at a 19 and 17 frame tonight when I get home. I don't think these frames are as aligned as CABALLOFLACO says, but it might be possible to grind away enough plastic from the G17 frame for the G19 recoil spring to fit. The picture below shows what appears to be a better alignment of the slide rails. I bring it up only because some of us, and you know who you are (welcome to the club), have a desire to tinker, to reinvent the wheel and make it custom, i.e. a Gen 3 "Glock 45".