DiGeM, You really will want to study the oiling system of your 261 as these were set to be run with or without full filtered oiling. Center of the block driver's side 1/2' oil line that has a hole/plug underneith, if the plug is pushed in you must run a filter, if it's out the filter is not needed. And if it's out, you'll want to push the thing in just over half an inch and I'd have the machine shop do that job as it's not easy to move that plug. It also may be easier to drill it out. When you get the plug 'IN' you MUST run a filter.
