RE: OS 91 Valve Spring question?
While I'm not familiar with your engine, i would saw "No" don't use that spring. It will bind up in the spring pocket.
I would suggest looking at the OS parts manuals for different engines. See if any of them use the same part number as your 91 does. There are many things that much be matched in a valve spring; length/height, outside diameter, wire diameter which translates onto the amount of pressure the spring puts on the valve and a few others.
Good luck on your quest.
Ken