Hi mate,
WOW...how much did you pay for it? They are a ballsy engine.
You can easily get a Kaaz or Mori shaft for this.
I have a Mori on a GX25 and it is awesome - I rate it equal with a Kaaz, so go with whichever is cheaper.
These guys should be able to hook you up with one:
DAVES MOWER CENTRE
287 Main Rd
Toukley NSW 2263
02 4396 3962
sales@dmcmowersaustralia.com.au
Ben.