I believe all 261's are high pressure oilers. The early ones, 54-57 use a by pass filter system like the 235 and have the smaller lines. In 58 they went to full filtration and started using the 1/2" lines. Note, because of this you cannot just block off the '58-'62 261 oil lines like you could on the 235's. If you do, you might be out an engine.
Steve O
