People have been looking high and low for 8 3/4 clutch style diff's ( powerlock ). Well, Doctor Diff has them back in stock now. Click the link below.
http://www.doctordiff.com/8-3-4-clutch-type-sure-grip-powr-lok.html
http://www.doctordiff.com/8-3-4-clutch-type-sure-grip-powr-lok.html