The best way to ID a '59 or later nailhead engine is by the production code. The production code is on the passenger side on top of the engine block infront of the valley pan. The production code is stamped upside down when looking towards the rear of the car. Here is where to find the numbers:
Here is a table that has all of the production codes:
The engine serial number is located on the drivers side and can also help in identifying the year the engine was built.
Buickman Award 2015
1957 Special 4-door Riviera (hardtop) model 43