Originally Posted by squidsix

It's not a weird idea at all. I have several favorite Frankensmith pistols.
Sadly, the combination you are describing typically does not work. I have tried all manner of combinations, and routinely carry and shoot a few of them. The ones that consistently work and shoot well are 3rd gen to 3rd gen same caliber (I have a 915 slide on a 6906 frame and a 4566 slide on a 4516 frame).
2nd gen to 2nd gen same caliber SOMETIMES works (about 2 for 6 in my attempts, but others have had more luck).
The 2nd gen to 1st gen does NOT work, in my experience. I have tried a 439 and 639 slide on 39-2 frame. No joy. Also 39-2 slide on 439 or 639, also no-go.
3rd gen to 1st gen also no joy in my experience. 39-2 slide on 3913 did not work, nor did 3913 slide on 39-2. (I have multiples of each and no combination of any of them worked for me)
I assume your 3914 slide will work with 3rd-gen pistols, and I have done the 5906 with 3913 slide, 6906 with 5906 slide, the aforementioned 45xx ones (many have done this and we had a thread going a while back about it), and 645 with 4566 slide strangely worked great but looked super weird to me.
If you are trying to find a home for your 3914 slide let me know.
Best,
Steve