Standard Budd socket for the lugnuts. The little screws that hold the box over the wiring are best ground and drilled in my experience as they are only sheet metal screws (but when they get rusted, you're stuck so replace them with stainless...).
Hubs, brake shoes, seals, bearings, drums, etc. are all the same as those on a M37 3/4 ton truck (M101/101A1 trailers) so the cross reference on my website for M37's and the list of parts suppliers is useful for the trailer as well.