Agreed, it's from May 1986 but like unworthy1, I'm suspicious about it being a replacement fork. During this period Tange had their own dropouts which they typically used on their replacement forks. While it may have been manufactured by Tange, the presence of Shimano dropouts would suggest that it was contract order fork.

BTW, I believe the tangs are FF4-2. The FF4-1 was longer, had straight sides and a rounded tip. This has the shorter length, subtly curved sides and chisel tip typical of the FF4-2.