I built a G17 frame from lonewolf dist and put an advantage arms 22 upper on it and love it. My son shot it and says it is the most fun pistol he ever shot. I don't know if anyone makes the upper for a gen4 yet. I think you can get the barrel from lone wolf for the 9mm conversion.
Retired USAF and postal. NRA Life member. Handloader since 1960. 10 years Deputy.