IBM XSERIES 235 HOT-SWAP PSU CONVERSION KIT - CONTAINS 2 X 560W PSUS HOT-SWAP BACKPL (02R188101) Power Supply "x40" Questions

...seeing about getting a UltraBase for it. I looked on ebay and I don't know what type to get. I see X40 Ultrabase X20, X61 and 570 UltraBase. Does anyone know witch UltraBase will work on my IBM ...