I just wonder whether it might be 337754?
Dunsfold have 33 of them but nobody else it seems have any.
I searched my NSNs for Guard, Splash, Rotor I removed all those that had no Rover part number & was just left with this one & the one we know about already.
Rover 551714 NSN 2540-99-802-1041
Rover 337754 NSN 2920-99-874-1823
Note the change of NSC to 2920 for non-aircraft engine electrical systems might suggest this has an FFR aspect to it.
I cannot find 337754 listed in any ISPL etc but there is a reassuring similarity to many part numbers that are very close in LtWt & S3 ISPLs.