Apparently the CH 640 is a scaled up 601.
The 601 span is about 25 feet while
the 640 span is 31 feet 6 inches.

Actually the 640 is based on the certificated AMD Alurus 2000 (yet another
zenith spin-off) Designed as an economical IFR trainer. The structures are
fundamentally different. Many of the parts for the AMD Alurus are the same as
the 640. Wing ribs, stab ribs, wing spar (640 has extensions on the wing spar,
stab about 2.5 wider) etc.
C. Smith