That model helicopter video!!!
That's not a model aircraft, THAT's a remote-control killer-scythe!!
No wonder the observers were back behind some wire-mesh
I could only suggest an Agni motor for its torque, weight and size. Not the HP/mass ratio of a model motor but will be much stronger. I'd look to mount it on the swing arm as near to the pivot as possible. Not perfect I know but volume is a big issue with so many bikes. My choice of batts would be a couple of Headway packs at 50V, 60AH, 20"x4"x6" long for $1300 apiece, so figure in import duties etc.
The Agni site has a useful page to work out power/weight ratio's with(out) gearing for offroaders etc.
Off topic but It also backs why I think "soldiers on the ground" should have one of these each with a stereo pair of IR HD cams and a small recoilless machine gun fitted. Then no sniper can run nor hide.