If you are referring to the oil filtration systems, the 1958-1963 261 had the capability to be set up with a full-flow oil filtration system. Yes, 1/2" NPT lines (two rigid metal tubes and two flexible hoses) were used. This setup was not a spin-on type filter (like moder filters) - it was a paper cartridge inside a metal canister.
Just to complicate things, the 1958-1963 261s could also be set up with a by-pass oil filtration system (or, no oil filtration system).
216s, 235s, and 1954-1957 261s had only an optional by-pass oil filtration system.
It is possible to use a modern spin-on filter-head (like modern oil filters) on the full-flow 261s. I have done that on the 1960 261 that is in my 1954 Suburban.
