I absolutely love that bike. It was featured in Cycle World mag last year. The article says that this custom was made by Dave Miller - a 70's motocrosser, motor builder, 5 times National champ cart racer, exhaust builder. His company DMC does dirt bike and atv pipes.
The article says that he took a modern Whizzer motor and sqeezed 11.7 ponies out of it!!! One-off piston, handmade head, modded crank and 24mm Mikuni...for 85mph top speed.
Sweet!