I ordered my replacement axle from
Trailer Axles for utility and boat trailers. Came to $162 shipped and arrived in 72hrs from order. The spring plates were bolted to the axle flanges so I could get the locations perfect the first time. I got a 52" WMF to WMF, which they had in stock. The factory axle on my Japanese Type 73 had a 52.5" WMF to WMF. Just put your trailer on jack stands, pull both wheels off and take a measuring tape from WMF to WMF. Honestly, it should be about the same, as the Japanese trailers are almost an exact copy of the 416.
I also didn't get any brake parts, but the axle is upgradable later. When I get a burr up my arse, and sick of using wheel chocks I will rework the brake. I was thinking of adding a hydro master to the factory brake assy and plumbing it into hydro brakes on the axles.