Like you said, I doubt that the fork is original - it has canti bosses for one, and there are none on the seat stays. Looks like a pretty decently built frame, but unfortunately I can't shed any light on the manufacturer. The Shimano dropouts and diamond cut in the lugs make me think Japanese.
edit: Maybe a Univega or Miyata, or Apollo?
Last edited by pacifico; 01-27-09 at 12:23 AM.