I just did this job. Assuming your builder got the "toe in" for the original axles correct - you need to try and capture that angle when drilling holes in the new axles.
1. Dimension check the external dimensions of old and new axles to confirm they are same. They should be - but production variance etc....
2. Dimension check the DEPTH of the old and new axles to the "ridge" that is the "highpoint" in the bottom of the axle. I found there WAS a difference - see later.
3. I took the old axle and put it on the drill press with the correct drill size in it and located the axle orientation on the drill table.
4. I then jigged around the axle with wood blocks so that when I withdrew the drill the axle sat unmoved on the table. Thus I had "found" the angle to drill the new axle to replicate the toe-in.
5. Remove old axle from "jig" and set new axle on jig.
6. I had to make a small adjustment for the internal depth of the axle or the gear leg would have bottomed out about 1/16" wrong.
7. Drill axle.
Same to drill the cotter pin hole in the axle. Jig old, then transfer jig dimensions to new.
Remember the "toe in" on the axles means they are "handed". You have to jig each seperately.