The Xbox ONE Durango Alpha towers are thought to exist of two types, Franken kits can be made but due to respect for Microsoft we will not share this information here.
The Durango Alpha towers contain multiple different GPU types all are AMD based normally. A second rarer XEON based Durango is thought to exist which was likely an Alpha1 Durango, Later kits were all AMD based. Unlike the later Durango kits this was in a white server case.
One was sold in 2012 on eBay by a user named SuperDae, not known to many is this was actually a franken-alpha made with parts bought on the likes of NewEgg, It's assumed this unit was destroyed. Source: https://www.theverge.com/2012/8/12/3238444/ebay-seller-claims-to-be-auctioning-a-microsoft-xbox-durango