Hi BalkanExpress,
The conversion can be done, although the main issue will be the stephenson excentric gear which seems to be on the middle-axle of the CO engine as opposed to the 3rd axle of the GKB loco... and to build a brand new working Stephenson distribution from scratch is way beyond sadomasochism...
For me the main problem is elsewhere: the GKB loco is such a sweetie that it would be a heartbreak to start chopping it

.. even in order to kitbash an engine most probably nobody has ever seen running in Greece!!
Anyway, let's keep positive and commiserate whoever starts this conversion!
Iossif