The only 767's US has are 200ER's. As I said, they're the 351K MTOW version and not the later 387K MTOW. US' have a max range of about 5300 nm according to Boeing (more eastbound, less westbound with prevailing winds). Hence the weight restrictions at times westbound.
Don't know which version of the -300ER TWA operated, but the 412K MTOW version has a range of about 6100 nm (again, more eastbound, less westbound with prevailing winds) according to Boeing. That's a bigger difference in range vs US' 200ER's than the difference in distance PHL-ATH vs PHL-TLV. To get to the same range as US' -200ER's, TWA would have had to operate 300ER's with a MTOW of no more than 382K.
US' -200ER's would be right at their still air max range on PHL-TLV. The prevailing winds would make the westbound flight weight limited all the time and moreso than ATH-PHL, while alternate requirements might cause weight restrictions eastbound at times. Plus, Boeing's range figures don't count any cargo weight - just passengers and baggage.
Jim