i'm on my second rad carrier, the first was fully assembled when i got it used.
this one i have now is semi disassembled, with a 4 pack of new bearings, 2 new seals, and what appears to be a new inner bearing spacer .....assuming thats the "big rod thingy" you speak of ???
that must be used !
it keeps the inner bearing race from collapsing when tightening the axle locknuts and spaced properly during operation.
if the rad your buddy got didn't come with one ?
clean and re-use your existing stock one.