You're talking about the spring which sits loose at the back of the transmission? Rests in a cast cup and is pressed on by the lever at the back of the transmission? Correct? If so, that is and important spring. It ensures that, when released, that lever gets pulled back away from the transmission and unloads any contact on the clutch throwout bearing. The little throwout bearing is intended for "momentary" use and won't last long under constant loading, even light loading.
I don't think the spring dimensions or force are particularly important. Anything would be better than nothing.
Patrick Hayes
Fremont CA