A904/A999 Forward Planetary Question

I'm in the process of ordering the forward planetary gears for my lockup transmission. WIT has them in stock that uses the 5" OD Ring Gear. Would that be the correct part to order? Also found one on eBay with the same description...

http://www.ebay.com/itm/like/291296046587?lpid=82

Part #: 12582B