Looks like a nice conversion. You may still get it at weight with those items you mention. Also, take a close look at any place you can grind on the model. Like cutting the hatch flanges narrower, canopy flanges, etc. Using aluminum bolts at all the places you can will save a few grams. I would maybe stay away from a BEC at this time. Any problem with the motor batteries and you'll lose RC power, not a good thing. You can use a smaller RC battery, since with no vibration there is much less load on the servos.

If you haven't heard, be easy for the first 5 cycles on the batteries. Stay away from a lot of full power runs, and charge at 1/2C. TP says it seems to help the cells by doing this little break-in.

Good luck with the project and if I can help at all let me know. And please let us know how it goes!