I've been trying to find a proper axle/differential setup for years and just purchased some new axles from O'Reillys last week and installed them over the weekend.
You're correct, the driver and passenger axles are different lengths.
There are two important measurements that can help reassure you that you might be getting the right axles:
1. measure the length of the axles
2. count the number of splines on the end that slides into the hub
and obviously make sure you get the correct bolt pattern (usually 5 or 6 bolts) to match up to the output shafts of the differential
here's a picture for reference
I actually had to order axles for a 93 infiniti j30 to fit the diff that I put in my s13 but they fit perfectly
good luck!