We thought the axles were ok on our '65 Safari- the angle was right (loaded and unloaded) and a trailer shop said that they were fine. Well, after a very long trip, we ended up with two cracks in the frame, one at each end of the axle mount plate on the curbside. It's fixable, but if I had replaced the axle before leaving, I probably wouldn't be spending as much "quality time" under the Safari as I am these days. We ended up with a Dexter, and it seems to be ok- but if I had it to do again, I'd go with the Inland RV Henschen. Cost is higher, but you won't end up with reversed brackets welded to your mounting plate like I now have, and you'll have shock mounts, which I still don't have.
So if you think you maybe, possibly, might want to replace your axle... do it, and save a lot of pain down the road.