EJ20K is pretty different.
IMO, if you've got a good running EJ20G set-up already, it's not worth the effort to convert. The ECUs are not compatable. The EJ20G is a 4 plug ECU and the EJ20K is 3 plugs.
The write ups on LegacyCentral cover exactly what you wish to do....Run a 2 channel coilpack with a 4 channel ECU. Basically....(4 channel ECU)>>(4 channel ignitor)>>join pairs of ignitor outputs>>(2 channel coilpack).