Take a look at this chart:

http://www.haydenauto.com/upload/HaydenAuto/Documents/Cat_Imperial/2007-imperial-fan-clutches.pdf

Find the original part number for your (or something similar) application. make a note of the measurements. If you need a shorter fan, play in the charts until you find one that fits your measurements.

We are brothers and sisters doing time on the planet for better or worse. I'll take the better, if you don't mind.
- Stu Harmon