I don't want to throw a monkey wrench in your plans but you may want to consider this.
I am preparing to put in one piece axles also. I have the axles but the 20 is still out getting rebuilt so I am on hold for the moment. In the meantime a friend was doing a similar job on a vintage GTO and ran into the following problem. He was using Yukon axles, and I have Crown axles and they both have the same defect.
If you look at the factory axle it has a nice smooth area were the inner factory seal rides on it. This area is cut a tiny bit smaller than the part of the axle where the bearing and the press fit retainer ring go. The new axles are not made that way. They are the same diameter all the way. He didn't notice at first, but once the bearing and retainer were pressed on, the axle was galled in the area the inner seal rides because the bearing and retainer are pressed over and past this part of the axle galling the metal in the process.
I would suggest marking the area where the seal rides like the factory axle and having the axles turned down a little and polished in that spot. The bearing is .003 tight fit and the retainer is .006 tight. So you need to remove .006 in the area where the seal rides to prevent the galling during assembly. .006 tight is very very tight!
Just guessing, but I suspect this galling is the reason so many people have problems with leaking axle seals. No seal will work on a rough surface.
Just my $.02.
If you always do what you've always done. You will always get what you've always got.