I need to change my rear driver side differential axle bearings and seal but I can't afford to put my 4runner out of work for more than a day. I have a spare axle but it's off the rear passenger side. Would there be a problem if I used the passenger side axle in place of the driver side?

 

The only difference could be the brake hookups. You might have to modify the brake backing plate to match the one that has to go. Or you could just swap the bearings.

 

This is very do-able in a day if you either have all the tools required yourself (bearing separator and a press), or if you can talk to somebody at a shop that has one and plan to bring the axle there after you remove it to get the old bearing pressed off and the new bearing pressed on. Aside from doing that, you're only looking at a few hours of work.