57 = Chassis Code - Universal
74 = Body Style - Open Body (Universal CJ-6)
8 = Body Style / Special Model Code - Universal
1 = Drive Code - Left Hand Drive
4 = Engine Code - F4-134 without Emission
280= Sequential Serial Number
From what I read, they made about 2000 CJ-6s a year, with a high point of 3521 in 1966. Production ran from 1955 - 81. It's a shame the VIN doesn't tell the year.