I do not use the droop screws as the chassis is not flat and can not be adjusted equally. I just use my MO5 M chassis TRF shocks 54000 on my MO5V2. If I was upgrading a MO5 to the new kit I would get the A parts and motor mount. For one piece arms I would use either Tech racing, 3Racing, Spice or Spec R items. The new motor mount does place the motor 1mm more towards the centre and also contains the 0.6mm spacer for the middle gear. I am unsure if this is required with the old motor mount. If you do not use the spacer the middle gear moves left to right which may effect the amount of contact space between the gears.
Just my thoughts, this way can use the standard inner a arms lower hinge screws.

I prefer the short square lipo pack in the new car, then I can add weight where I want too. My shortie pack weighs 202 grams to which I have added a 10 gram lead weight.

Battery choice is up to yourself. My shortie pack is offset to the non motor side of the car.