Brushless motor worth it?

[Lil Giants]

Sounds like you need a better esc for smoother starts, what I've used in the past is Mtronics 15A Marine esc, really smooth start/stop with brake.

Using brushless... to find anything that will fit & still have a low KV rating probably doesn't exist without a speed reducer to get the rpm down... that 80 turn motor you have is a 12v motor that you're running on 8.4v, I'd guess it's spinning at 6000rpm - maybe less. Those Integy high turn motors are a direct fit to the 3spd trans, to do anything different will definitely add length & probably require adapters to mount as well.