There is a subset of the 763ER ships that is configured with crew rests, winglets, & GE engines (better SFC over PW) for the longest of the 763 trips like JFK-AMM, TLV, CAI. They are ships 1607-1613, a total of 7 ships. These will likely be first to get the mods, but I wouldn't be surprised to see other 763ER's getting the same mods eventually, it just makes sense to deploy them on the longest routes first.