When rebuilt my K0 750 18 months ago I had this very discussion with Hondaman. Both the K0 tranny and a later tranny that came with the bike were in excellent shape. I ended up gong with the later tranny because he told me that the brass bushings in the K0 tranny were subject to premature wear. Other than that, either is equivalent. We did not talk, at the time, about shift fork drums.
Hope this is helpful to you.
Patrick