I have run a WWA Mini kit on a full bodies karni, so I'm surprised it didn't work for a mini. Please note that because of the karni's milling, the pump kit is able to wobble side to side (Karni has a round body, where standard has a rectangle body. To stop this, use teflon tape or loc-tite. Otherwise, it could be a problem with the threading of the front block when the karni was cut down.
Markers: FBM Teardrop Cocker, CCM'd Pump Karni, CCM'd pump 2K6 Black Magic, Sleeper A-5, Twin TiPX pistols and a now freakin' ULE Automag!