If your 261 has 1/2" NPT holes for the oil filter lines, you have a 1958-62 261 that was set up for a full-flow oil filtration system.
Do you have the original full-flow canister? If so, it will also have the 1/2" NPT fittings. Go to another parts store (a NAPA that makes hoses, should be able to do it). Or, look for a heavy truck repair shop.
