rare fan?

Part number 2863213 would be stamped on one of the blades , for 383/340- 68/69 used in all body/engine combinations
part number 2863215 for 340/426 -69 . these parts are also used on C-B-A bodies, with different engine and cooling options so they are not rare. Looked this information up in my 68 and 69 parts books. . The difference is in the pitch of the blades 1.5"- 2863213 or 2.25"- 2863215
There is a 7 blade number 2863224 in 69 listed for all bodies and engine combinations ,nothing listing a special one for SS application. Hope this helps.