What year 261 engine do you have?
1954-1957 261 engines were set up for by-pass oil filters (and have a smaller line, as used in all 235 and 216 engines).
The 1958-63 261s could be set three ways:
- no oil filter
- by-pass oil filter (smaller diameter lines)
- full-flow oil filter (1/2 NPT lines - the 3/4" lines you refer to).
The full-flow oil filter should only be used on a full-flow 261 block/engine.
It looks like your engine uses a by-pass oil filter. Do not try to use/adapt smaller lines with that full-flow 261 oil canister with large lines/ports.
