Peerless 820 axle questions

I hope this is helpful to others as well as myself. From what I've been reading, the Peerless 820 is a pretty HD transaxlle. I'm looking into using one to build an UTV built from scratch. I see a lot of info about installing the -017 kit in a standard 820-XXX transaxle. http://www.heymow.com/index.php?topic=14202.0 What is the real purpose of this? I also see installing the high speed gear set from http://roms-peerless-transaxle-supply@ecrater.com/
If I only want/need 30-40 MPH out of the transaxle, would I be better off with a pulley change or doing the gear swap? Next question is about engagement. Instead of using a drive belt like the OEM does like a clutch, either engaged or disengaged,would it work better to use a centrifugal clutch with a pulley or chain drive to the 820-XXX transaxle? I see I'd limited on the centrifugal clutch pulley size. I'm not sure it would give enough belt contact if I went 1:1 because of the limited pulley size available for the clutch. I want to keep it as simple as possable, no jackshafts ect, just go from the engine to the transaxle.

My group has done the gear change on the peerless 820s... it works pretty good, but the shifter keys are under considerably more stress, and wear out a lot faster. Ours top out at 45mph by the way.

As long as the clutch is on the slack side of the belt, the OEM style clutch works fine. We did upgrade to 5/8" belts as well which improves grip and lasts longer.