According to Engine tech and Sealed power the exhaust and intake springs for 1954 to 1962 261 engines are the same part#. Engine Tech ERV709 and Sealed power VS434. I did discover that 235 engines of these same years used a different valve spring # than the 261, but still only 1 spring for intake and exhaust.
Also the free height (uninstalled height ) of the springs is different. 261= 2.250 235= 2.160 according to sealed power.
I wasn't born 21, so, obviously I don't know everything.
Respectfully
