If you don’t mind my stepping in…
Sound Lab speakers are modular now in four different ways:
1. Frame: wood (M), furniture grade (A) and tubular steel (U)
2. Radiation angle: 45 or 90 degrees
3. Height of panel
4. Number of “cells” across. Standard configuration is seven across. There are now three, four and five cell versions.
In answer to your question, a G9-5C is a foot taller and somewhat narrower than what is effectively a G8-7C. The new Japanese website has an illustration that might help:
Click this link and scroll down to specification: