Here are some close ups of the drive unit I have mounted on the test stand and a scanned copy of the Installation and Removal Document. The only difference is that my unit doesn't have the Idler pulley. They eliminated that pulley prior to my kits production.

The reduction drive allows you to swing the the huge 4 bladed prop at 3000 RPM to give you that real 51 prop whoosh sound in flight not to mention that great big 4 blade look.