Sorry I can't help with the exact cg location, I traded off my G-Shark last year. Just use 28 to 30% of cord.
The canopy can be had from Tower if you search their replacement canopy section. Look for Great Planes and Midwest 1.60 scale Extra. With a trimming of the red section, it will look like factory. The cowl is still available from Fiberglass Specialties.
http://www2.towerhobbies.com/cgi-bin...?&I=LXSF57&P=0
http://www2.towerhobbies.com/cgi-bin...?&I=LXEYZ5&P=0
http://www.fiberglassspecialtiesinc.com/catalog.htm

I flew mine for over 5 seasons without a hint of snap. Your plane must have been too tail heavy when you saw it fly.
The tip stall can be corrected by reflexing both ailerons up 1/8". Mine landed about like the G. Stinger with the reflex and ST 3000. So many pilots were having problems with nose over using the 38 to 50cc gas engines; that's the reason for the MkII with a couple of inches longer fuse. If you'd drop down to a lighter 1.8 to 2.10 engine, I know you would have an easier plane to fly. Mine also had the rudder pull/pull up above the wing.