DL operates a 777 on DTW-ATL and ATL-DTW daily. I took it back in April. I checked a few dates, and 1619 is a 737-800?
The 777 I took did not have lieflat seating, it had the older business elite seating. I took a 777 from ATL-LAX last year (that continued on to SYD) that had the lie flat seating.
Suggestion... if you see a flight that it's operated on within the next month, jump on it. Otherwise, you know how DL is with schedule changes :P