If you read the 1957 parts book correctly it says:
"1950-52 Pass with Power Glide 3835777", which is a hydraulic lifter engine.
"1953-55 W/PG, and 1956-57 ALL". 1953-55 W/PG is a hydraulic lifter engine, and 1956 started the shorter lifter that matches the length of the hydraulic lifter, so it uses the same push rod.
The 3835777 push rod is different mainly in that it is grooved across the bottom face (see link in above post). In 1953 they dropped the groove, thus a different part number.
