The books I have show the large sight glass carb on the F125? I am not sure if that 125 is a typo in the book or not. The F135 started in October 1, 1959 with engine number F 120001. Prior to the F135, the engine was an F120 (120 HP at 3600RPM). All early carbs have a date stamp on the rear of the carb near the base. Here are the ones I can get to (-5 outside and the hoods are frozen shut) for examples:
Blue window -1958 - 1966
Gray window - 1967 I think
no plate - unknown
1964 FJ40L
4B 4 = February, 4, 1964
not original motor to the truck
6C 3 = March 3, 1966