I had a Gen 3 26 that I changed the ejector and put on a complete G33 gen 4 slide assembly. So without any question a Gen 4 subcompact slide assembly can fit on a 3rd gen subcompact frame. I am also using 357 sig mags. Oddly I had one that I put in a new mag Glock oem mag spring in the Gen 3 mag (no ambi) with the Gap floor plate and it now holds 10 rounds?? I have another new gen3 (no ambi) mag with the pearce +1 extension and it holds 10. The 4th gen ambi mag only holds 9 rounds. I found...
G26 Gen3 converted to Gen 4 G33
G26 Gen3 converted to Gen 4 G33