Not sure on your setup there... as I am no expert, but I am converting my Boomerang 40 now also... Plan on putting in a Turnigy 42-50A 700Kv motor, 12x8 prop, 60A ESC, 4s 4000mAh battery. Conversion seems to be running very smoothly, and just finished an access hatch to get into the battery etc... I have also added some air scoops to direct the air into the cabin. Progress pic below. I have just finished painting and reapplying the black window, to make it look the same as the original.
Click on image for enlargement.