Hi Maxpower,
Please consider the following.........
The HF motor normally idles around 900 RPMs [800 to 1000], the clutch you are considering engages at approx 2000 RPMs. The motor normally operates between 800 and 3600 RPMs, meaning you will need to rev from 900 [approx] to 2000 RPMs before the clutch engages. The span from idle to engagement is over 1000 RPMs [a lot!], and is almost 1/3rd of the entire range. The clutch you referenced is also chain drive [#35] output.
We had MaxTorque design a special clutch for us to engage within a few hundred RPMs off idle after we divided the motor output to our clutch, therefore a stock "over the counter" unit just won't work correctly.
If you use the clutch referenced and use the chain drive from the motor to the wheel without a drive system in the center the needed rear sprocket would have to have at least 66 teeth to end up with an 6 X 1 ratio [I doubt you will climb many, if any hills, or pull a heavy rider at that ratio].
Keep us posted on your progress.
Have fun,