The Spike grips wrap around the frame instead of attatching to the sides so there's no room for error. Also, the way the magazine is designed the grips have to be a very specific thickness to still allow the mag to slide in and out freely.
KWC should be treated as a no-go for anyone expecting to mod it. Also, clarification on the Metal Slide issue. KWC made two types, a .177 mm gun that fires steel BB's, and one that fires the plastic Airsoft pellets. That gun is the version that Cybergun licensed, the version that fires the steel bb's is the one with the metal slide.