Thurlow, The Nemesis diffs are beefier in construction, they have an aluminum case and housing the outdrive cups are heavier and the outdrive bearings are larger. They are getting harder to find the 'Bay but you can order them from CEN Direct without the Pinion as the pinion is the same as the Genesis, But CEN was wise in using the same bulkheads on the GST so you wont need those all you need are the Diff Kits..

[link=http://www.cenracingdirect.com/index.asp?PageAction=VIEWPROD&ProdID=373]CEN Direct Nemesis Front And Rear Diff[/link]

[link=http://www.customrccars.com/product_temp_trial.asp?id=1555&cat=21&custom=0]Custom RC Parts Nemesis Front Or Rear Diff[/link]