RE: Electric Motor ?'s
That surprises me because the Goldberg Electra has been shipping with that same 550 motor since it was introduced many many many moons ago. I remember the Electra being around when I was a kid.
If the motor doesn't fit, I'd complain to Goldberg first and foremost. Somebody messed up the assembly of that plane, and they should be obligated to fix the issue. I've heard of including a motor that wasn't powerful enough, but never a motor that was too big to fit in the airframe. That's absurd.
Geared, with an 8-cell battery pack, I don't see why the Electra wouldn't fly on the Cobalt 400. You can get a planetary gear drive so the motor will fit in the slender fuselage, and run a big diameter prop. This plane flies slow, so you need lots of thrust, not speed.