Could anyone spring into action post and cut me a brake? See what I did there?

[thedudeabides86]

Soooooo, working on this ol mess. I've got all the parts off and installed the new wheel cylinder. I cleaned up the back plate. The old wheel cylinder leaked and prevented me from bleeding the brakes efficiently since the pedal just dropped down to the floor. I got all my parts at O'Reilly down the street and for replacement spring kits they offer an 11" or 11.5". How do I know what spring kit to use? I can't find anything anywhere that helps to determine what size kit I need. Anyone help me out? I'd really appreciate it.