Thats amazing Chi !!!
Just had a look at the the Psycho billy that shows it really well.
Wouldnt the transmission have to be REALLY off-set to accomadate the rear drive (so it only lends the design to a belt/chain primary drive)
I've been watching the American chopper series:
http://www.discovery.com/?channel=DSC apart from the red frame on there that looked stunning along with a Carb built in the shape of a fire hydrant (REALLY - it was awesome).
Some of the engineering and design work is stunning but it does worry me a little when something does not fit quite right in a frame, so they simply grind a bit out and fill it back in again
