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If you look at seatguru.com you will see that:

Delta is in process of converting its 767-400 fleet from conventional seats to flat-bed seats in the BusinessElite cabin. This probably means there is no guarantee which type of seats will be on your route, but I think DL has set aside most of he flat-bed equipment for flights to/from London:

http://www.seatguru.com/airlines/Del...-400_Trans.php

http://www.seatguru.com/airlines/Del..._767-400_B.php

Air France operates four versions of 777, and all have lie-flat seats in Affaires Class:

http://www.seatguru.com/airlines/Air...77-200_new.php

http://www.seatguru.com/airlines/Air...ng_777-300.php

http://www.seatguru.com/airlines/Air..._777-300_B.php

http://www.seatguru.com/airlines/Air..._777-300_C.php

If you're not clear on the difference between "flat-bed" and "lie-flat" there is a generic explanation with diagrams on SeatGuru.

I think you will receive better answers to this question if you search in the Air France and Delta sections looking for information about the specific type of aircraft that Delta uses on this route and reports of the service on both AF and DL. It's better to decide for yourself than to rely on replies which offer a dismissive conclusion with no explanation .