I'm running the bafang 750w version on a 73mm bottom bracket. You need to make a few spacers and use longer bolts to make it work but it is really quite easy. See in the picture the 5mm thick nuts I have drilled out as spacers, you could use washers...
I have an 8speed cassette and the chail line is rubbish. I had to put a chain keeper on top of the chain ring to stop the chain coming off.
1 locknut works fine , no locktite used, just brute force. Done about 700 miles on it. Awesome kit.
The 750W 48v version is now available from Alibaba. Single unit 440 USD, shipping to UK 75 USD, so about£320 total, plus any import duties etc.....
Not sure if this will be the same as the 2014 version or not. Anyone?
I think if this was coupled with a NuVinci N360 rear hub it would make a very capable bike, IMO.