Chad, there will not be a part number. There will be specs that the axle
is built to. If their distributor in Alaska also does the work, let them do the measurements. If not get them to suggest someone and let whoever that is take the responsibility.
The only change I would strongly suggest is get the bolt on brackets or (AP kit). It will raise you the thickness of the metal bracket and mean that if anyone ever has to change the axle
again it will be a simple process that does not involve cutting or welding.
You may want to change what the axle is rubbered to, some of the early ones were built for 1200 lbs, we know the trailers come in higher than that. See the trailer weights in the real world thread.
Trailer Weights in the Real World