I don't know the identity of the manufacturer but the format is consistent with the Japanese source used by Bianchi in the 1980s. The frame itself is from June 1974 while the fork is a standard, off the shelf, Ishiwata product from May 1974. Given that the fork is Ishiwata, the frame tubing is likely Ishiwata too. Consequently, we may be able to determine the tubeset from the inner diameter of the seat tube or the diameter of a proper fitting seat post.