I sure got a laugh out of the other bike pics your posted, like the snowplow and grocery cart bikes.
Not sure if you found the link so here it is:
Mark Eckert Markolounger
He basically combined the rear of a mountain bike and the front of a bmx type bike. He had to put two chains together and an idller sprocket in the middle. One thing I don't think I'd like is the tiller type steering. Thinking I could put a u-joint along with a support bracket where the handlebars currently mount to make something more natural feeling. I've got an old mountain bike already and should be able to find a smaller bike for the front. I'm kinda anxious to start on it but I really need to get some other projects done first.