With such a limited supply of Rolls Royce powered 767's would FedEx really want them? IIRC QANTAS and British Airways are the only major operators of 767's with these engines.
Will look for the link but Qantas has been selling 767s to AtSG for conversion to freighters and recently announced mass retirement of the 767 fleet over the next 8 yrs, so i guess there is a pretty large supply out there up for grabs.