Here are my two, KSC/KWA Glock 18c and 19. Not heavily modified but both have Guarder steel mag catch, Guarder recoil rod and spring, uprated hammer springs and the 19 has an aluminum rocket valve to replace the standard plastic item and a mag extension from a 50rd mag.
I use an RA Tech co2 mag with the 18c, I get about 80 shots on one bulb, noise and blowback is much improved! I've added an extra length of spring to the recoil rod to help cope with the extra blowback power the co2 gives. The 19 is over ten years old and still going strong, it has the full Glock trade on the slide whereas the