Classic/Antique Car Repair: 1951 chevy 216ci engine, todays cars, bypass filter

Question
Why do mome 216ci engines have oil filters and some dont.  My 1951 chevy doesnt have one.  I see pictures of some that have them and some that dont.  Any help will be appreciated.

Answer
The oil filter on these cars was an option like the heater or the radio. Many were added on at the dealership at the buyers request. The filter was a bypass filter an unlike the filters on todays cars that filter 100% of the oil the by pass only filtered at best 30% of the oil.