rear axle length

i am working on a 55 buick for a good friend , changing trans and rear to accept a open driveshaft , bags and 20s and 18s .i need a rear axle . 57 or 57.5 hub to hub , prefer chevy bolt pattern 5x5 ( i know i can redrill bolt pattern )dont care about what mounts . anyone know what year,make , model .
before i head out to the boneyard to start measuring

Okay kenny, a guy like you needs references like these.

http://www.teufert.net/other/rear%20...dimensions.htm

http://hiqties.hypermart.net/chevyrear.html

http://hiqties.hypermart.net/9inch.html

bob ,real good sites , thanks big time