I don't remember any fuel imbalance limit other than 600 pounds. I checked all my manuals and can't find it. But it could be due to UK certification or because it was a FC530 A/P. All my books are for the FC200.
Also it became a requirement last year, but has been a prefered option for at least 4 years that engine out landings are make with flaps 20, not full flaps.
I don't believe that the Y/D was that much of an issue.
Unstablized approach with the 'wrong' engine inop, can make for an interestinjg time.