With nothing eles to go on I'd say 1981.
258's with the C code were built between 76 and 89 according to the info on the link I posted earlier. So an engine could have the same number and be built in 1977 but it would be a first generation 258 and would have come from the factory with 1/2" head bolts, a steel valve cover and a cast Iron intake manifold that would be bolted together with the exhaust manifold instead of the separate aluminum intake that came in 1981. but as I said before, heads and manifolds can be swapped, casting numbers are one sure way to tell. Here is a list I found, I haven't made any attempt to verify it yet.


1975-79 258 4.2L 1/2" Head bolts

Blocks: 3227445 and 3224098
Head: 3227258
Crank: 3214723

1980 258 4.2L 1/2" Head bolts

Block: 3235077
Head: 3227258
Crank: 3214723

1981-85 258 4.2L 7/16" Head bolts

Block: 3235444
Heads: 3933000, 3224480, and 3241656
Crank: 3235477

1986 258 4.2L 1/2" Head bolts

Block: 3227444
Head: 3933002
Crank: 3235477

<img src="/forums/images/graemlins/cheers.gif" alt="" />