Re: V twin - 50cc bike...
I guess it would require a stretch or limo bicycle frame to accomodate it. I'd probably buy an engine with a faux rear cylinder. I had been trying to figure out how to attach a second, empty cylinder on my bike to impersonate a v-twin.
The smallest genuine v-twins I've seen have been the 250cc Lifan or Suzuki Virago.
“You're only young once, but you can be immature as long as you like" -Unknown