Found a decent scale today, so I measuered some weights.
The X-UFO, complete with batteries, is 320 grams.
Battery is 83 grams,
The Gyro is 16 grams,
and the Transparent dome is 5 grams(with the doublesided tape that held it in place.
I found a replacement 11.1V/800mAh Li-poly pack at approximately the same weight in a netshop, so I won't save any there. (I could have gone for a 400mA pack, at about 40 grams, but then I would still be struggling with a 4minute fligh-time. Which really isn't long enough when testing stuff)
The replacement gyro is 2 grams, so a theoretical saving of about 5% of the total weight.
As I won't have a RC receiver built into the electronics, I may be able to save a few grams there, too.(Any saving depends on how good I'm at designing double-sided PCBs with surface-mount components.)
I know that I won't be needing all the connectors that the original PCB had, but that saving will be minimal.