I think Ed Boysun built a oil bath chain reduction case for an auger and was running it with a D-21. Geared so tractor did not have to run at full PTO engine RPM and to keep it in the power band. https://talk.newagtalk.com/forums/thread-view.asp?tid=26553&posts=1#M179901 Some pics on his web page. http://www.boysungrain.com/shop-projects.htm Was far less than this commercial unit was going to cost. http://rodono.ca/Content/FITS_ALL_1000_RPM_ONLY_TRACTORS/ | 
1000 to 540 rpm reducer
