1958-1963 261s had the capabiluty for a full-flow oil filter (1/2" ports on the block. Some 58-63 261s can be set up with by-pass or full flow (and if they came with no filter, they needed no filter. If a 261 ever had a full-flow set-up, it has to always ever after have a full-flow set-up (or have an external line connecting port holes).
Post head&block casting codes and date casting codes.That engine in the first posts looks to have a by-pass oil filter and by-pass 3/8" lines and block ports.
