Rhammami,

Dell no longer publishes EOL details for the Poweredge lines since about the 11th or 12th generation of servers, but it is pretty standard that a server can be warrantied up to 5 years from the ship date. That can be extended on some basis, but that is based on part availability. 

Sorry I couldn't get you the specifics you requested, but I hope this helps.

Have any document confirming the continued marketing of POWER EDGE R660 and POWER EDGE R760 , specifying the end date of marketing.

Unfortunatly there is not. You can find system specific dates if you go to the dell support page and enter the systems service tag.