I've built 5 CG Ultimates...here are the mod's I would do, in no particular order:

-Fiberglass cowling and wheelpants from Stan's Fiberglass...ask to make them "contest light"
-Aluminum gear from fiberglass specialties, but NOT the cowling, etc...heavy white fiberglass with pinholes...
-barn door the ailerons...i.e...box them in with aileron stock about 1 inch at the tips
-plywood reinforcement at the cabanes on the upper fuselage piece
-taper the tail surfaces with a razor plane
-use 6 inch wide balsa to sheet the tail to avoid having a wood seam
-ditch the crappy engine mount for an aluminum one
-YS 1.40 all the way!
-goes without saying...two aileron servos instead of the one
-cut off the rear plywood turtle deck sheeting and carve balsa farings so you can assemble the plane after covering
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-Some extreme mods:

-thin the sheeting on the wings and tail to 1/32 instead of 1/16
-cut out new balsa top and bottom for the fuse to save some weight