I ordered it from Pistonbikes $500.
Web Site info : Arrow 4.5 HP Street RacerMotor. Built on the Grubee Skyhawk Motor. Each engine is worked on and built by Dave Rust of Arrow Motorized Cycles - ( arrowmotorizedcycles.com ). Dave and the Arrow Motorized Cycle Race Team have been tearing up the So Cal race scene for awhile now. Here is your chance to get your own race motor."
They talk in terms of 4.5hp due to head and air intake upgrades. Not sure about how many cc's.
I have as big as rear sprocket as I could find for 415 chain. I"m still breaking in the motor so now way of knowing the top speed.
I'm looking for low end and mostly slow as I plan to ride it mostly in sand at our lake.