1979-80 by the S/N
The 64-2 was produced in 1977 and appears the 64-3 started production the same year. I do not know if they produced both models for a period of time.
Please comment Flyfish or Layton.
The -2 was a 2" tapered barrel and the -3 was the heavy barrel versions. Both were produced concurrently until they became -4 and -5 versions with the next update in 1988.