Found online:
Yes, you can put a 17/34 slide on a 19 frame. Here’s how.
ADVICE
This keeps coming up alot lately, so I figured I’d give a quick explanation, and hopefully this clears it up for people.
Yes, a Gen 3 17/34 slide will work on a Gen 3 19 compatible frame, with some changes.
Three, to be exact.
The only issues that stop this from happening naturally are the locking block/barrel lug mating, the guide rod length change from alleviating the barrel issue, and the gap between the end of the slide and the frame (that covers the recoil spring/guide rod). These can be accounted for.
Issue #1: The Barrel
You can alleviate the barrel issue by either:
A) Getting a Lone Wolf Distributors barrel (19l for the 17, 19xl for the 34)
Getting the Brownell’s 19 Long barrel (and their 19 long slide... only 17 length, no 34 available), or
C) Getting a Gen 5 17/34 barrel (the lug pattern on the Gen 5 matches the locking block of the 19, and does fit properly inside a gen 3 17/34 slide).
Issue #2: The Guide Rod
Due to changing the lug spacing, you will need the extended guide rod from Lone Wolf (example here)... with the lug pattern shift on the barrel, the standard guide rod will come up a little short. (Shout out to u/PopPopSun and u/gammaRay-Ray for pointing this out)
Issue #3: The Slide-To-Frame Gap
To solve, get the Lone Wolf Distributors slide adapter (link).
Those are the only changes you need to make. Otherwise it’s just getting the appropriate parts (gen 3, with upper parts matching the slide, and lower parts matching the frame).
Hope that sorts things out for everybody. Have fun building.