if you get the full size lower you can build it as a model 17 (9mm), a 22 (40s&w), or a 31 (357 sig)
if you get the compact lower you can build it up as a model 19 (9mm), or a 23 (40s&w), or a 32 (357 sig)
if you get the sub compact lower you can build it as a 26 (9mm), a 27 (40s&w), or a 33 (357 sig)
this is assuming you want the conventional length slides and calibers, not any of the long slide versions or the .22 kits…which you can also use