I think Delta have 10 ex AA 757-200ERs on the way, to be used on Transatlantic flightsm.
As for RYR restrictions at LDY, I'm not sure the engines are the problem. Most of the 738s have the 26k rated engines, only some have the 24k rated. I thought brakes were more of an issue with higher temperatures on the short runway and the turnaround time?