I have no clue I never even thought of that.
I'll try asking the guy from page 7 that gave the equations for which motor to use.

Also If you go with an electric motor with specs similar to the ones on page 7 like 24v 200w they are easy to find in a wide variety since they are used for electric scooters like Razors.

So what are you running on your bike.
2 or 4 stroke and how do you plan to spin the power source?

I have got a 4 stroke and am using a Firebelly Hardbox(very sturdy by the way). I am unsure of mounting though because Evan just came out with a shift kit for the Hardbox and that would totally change the sproket and mounting location of the powersource.

The only thing I can come up with is to fabricate a custom bracket, mount it on the frame then spin it off of the drive chain and base the rpm's for the power source on my average top speed. Of course I would also suggest a rechargable battery and a voltage regulator.