There is a year stamped on the cylinder head above the exhaust ports on the head. It looks like a 9/? with the "?" being the the other part of the year.
Example? If the engine was manufactured in 92 the stamp wpuld look like 9/2, etc. etc.
The thing is that sometimes a year stamp or 9/1 means the engine was made in 1991, but is actually still a "1992" model engine, or "second-gen" engine.
A pic of a 1988 model D16A6 Honda cylinder head:
It's the stamp on the right side of the pic - the 8/8