I'm not sure which manual you're using ('55 Chevrolet perhaps?), but here's the manual page from the '55-'59 GMC Maintenance Manual http://chevy.oldcarmanualproject.com/gmc/5559mm/5559mm173.html
It shows how the spring mounts better than the Chevrolet manual does.
I'll see if I can get a good pic of the spring on my Chevrolet, there is a possibility they might have sent you the clutch pedal spring, which is similar, but longer.

Bill Burmeister