Peter
I think you may be gatting confused a little. There are 4 different models in the Greenley family. The original Greenley was designed around a Zenoah 38 and has proved very sucessful with hunderds of plans sold before I decided to make the plan available as a free download from the Ghost Squadron website
http://www.ghostsquadron.co.uk.
From the original Greenley other bigger models have evolved more specifically modified for glider towing and the fitting of larger motors. These as not just scaled up original Greenleys but have been modified with different moment arms and nose lengths to suilt the task they were designed for.
The original Greenley can be built under 7 kg with a Zenoah 38 and a foam wing and with care in wood selection (especially the tail surfaces) and a proper installation will require no lead to balance.
Hope this helps.
John