Also, if you ask someone that installs them, they will tell you that you need to replace the u-bolts as they stretch when you tork them down and a lot of times, they have been rusted on there for years and sometimes get weakened when you pull them off.... then there are those that would reuse them a time or two... (have done that too)... bottom line, new ones are cheap insurance that you won't have any issues due to one of them breaking...
Also, make sure the yoke on the pinion is the same between the 2.