I am open to learning something new, and also admitting I was wrong when I am presented with clear evidence. In the interests of full disclosure, much of what I write in my frequent posts has been gathered from reading other peoples experiences.
In the absence of any type of throttle ramping/snubbing (the rider snaps the throttle full on, but the power comes on in a gradual curve), I believe an IGH should remain an option for the BBS02, but for the 50V X 30A = 1500W that I feel this kit is suited to start at (Christerljung is running 100V), I would not recommend to anyone to use an IGH. The ability of the motor to use several gears is a huge benefit for off-road use, and any chain/sprocket system needs to have a chain that is flexible enough to be nudged sideways.
Roy's eCortina used a heavy-duty BMX chain (with 1/8-inch wide rollers between the link side-plates), and three cassette sprockets at the rear. I suspect he might have been able to squeeze-in 5 gears, and this would be my next most desired experiment.
For a big block left-side-drive, there are several options. Of course Luke established that #428 works well. Also, #415H looks good on paper, but few people are trying it yet (difficulty adapting sprockets?). From the archives, here's a tip from farfle:
#219 chain and sprockets would be pricey, but would have no problems with high power.If you are willing to machine stuff, #40 industrial sprockets thinned to 3/16" run #415 chain great. Its what I run 24-HP through on my bike