Hi Black Panther,
There were a lot of options on clutch systems "back in the day". Whizzer [vintage] offered a manual clutch with a 5"/3.5" or a 5"/4" pulley. The 4" output pulley was designed to balance the 20" Sportsman ratios. The stock ratio on a 24" Whizzer Pacemaker was 9.15 X 1 and the stock ratio on the 20" Sportsman was 7.96 X 1. The 24" Pacemaker would travel at 40 MPH @ 5130 RPMs, and the 20" Sportsman needed to turn 5355 RPMs to reach 40 MPH. Whizzer also offered the automatic clutch in both pulley sizes. For a short time they even offered a 2 speed automatic [Bi-Matic].
Whizzer [and thier authorized dealers] now offer the automatic clutch in three output sizes, a 50MM [1.96"], 70MM [2.75"], and 90MM [3.54"]. Final ratios are 16.93 X 1 [should be able to climb the side of a house, but very low top end], 11.78 X 1 [great for heavy riders that ride in the hills or mountains], and 9.04 X 1 [great for average or light riders].
I used the 50 MM on my record setting Sportsman at Dawson Springs, KY in 2008, but changed to 70 MM in 2009 [opps, went even faster, and set new records]. I use the 90 MM on all my street Whizzers because I like to cruise without the motor "wound up tight".
Have fun,