Simply use 25% of the mean aerodynamic chord (MAC).

That may well prove to be the right spot but even if it is not you will live to fly another day
and can make adjustments from there.
You will do that even with the factory suggested CG as it is simply part of trimming the airplane.

The old saw is "Friends do not let friends fly tail heavy."
The above suggestion precludes that yet is well within reason .

If you are not familiar with the MAC go here: http://www.airfieldmodels.com/inform...amic_chord.htm

BTW the model IS currently available http://ecsvr.com/abm/shopexd.asp?id=36