Might need to narrow axle housing

I have a question about axles. If you are going to narrow the housing do you need to find an axle and narrow to that width or can the axles come in or be modified to any length? Does that question make sense?

You need to do one of these things...

1. Narrow the housing to the same width as another stock axle- ie, narrowing a truck 8 3/4 to A-body width and running A-body axles

2. Have the axles shortened and resplined to fit the narrowed housing. Just FYI though, not all axles can be shortened and still work. Some of them taper or have steps in diameter, so they won't be the right diameter once they're shortened.

3. Buy custom length axles.