And now two of them are possibly installed on Silk Way 744s
https://www.airfleets.net/photo/Silk...13321_b747.htm
https://www.airfleets.net/photo/Silk...89359_b747.htm
https://www.airfleets.net/photo/Silk...94470_b747.htm

I guess there's a chance that the engines might be ex-Cathay and still in their grey livery. However the that there are some BA blue parts on other engines (and all the other three on 4k-SW008), I would strongly guess that they grey ones are very likely two of the three ex Negus.