Assume you're talking about the 2-class 767-300
16AB and 17AB are blocked for crew rest. 16DEF are often blocked because they're the bassinet seat I think. 17DEF and 16KL and 17KL should not be blocked nor should anything in 20.
Note that this is just for TATL flights. If the 767-300 flies domestic (and perhaps on IAH-LIM) there is no crew rest requirement.