I have had good results bolting to a flip/flop-
you need a large flange hub with smooth undrilled sides, so you can drill the six hole pattern- and of course the sprocket has to have that pattern- it helps to have one with that already- if steel especially- because that's a tough drill-
the alloy hub on the other hand is easy- and plent strong- the six holes constitute less metal gone than most pre-drilled patterns. Here's my thread on it.
Of course, this doesn't freewheel- Boygofast on ebay sells a freewheel sprocket and huibs, but then you need a pull starter, centrifical clutch, and then wider cranks
With my set-up, if you use a 415 Trike chain, the pedalling resistence is minimized- really not too shabby-
I've thought about posting a thread
"I'll bet my motor bike pedals easier than your pedal bike!"-
that would apply to quite a lot of bikes out there at least
heres a great inexpensive 34 alloy sprock with the six inner drillings- a 66 should pull most riders on street use, if running correctly otherwise and not too massive climbs. I can cruise at 30 still not wide open throttle.
This thing is featherweight- get some M5 x 20/25 TITANIUM bolts and you've save a ton of weight compared to a kit set-up.