Is it a Big Block or Small Block (1964 - 1990) Engine?

There are three ways:
  1. A big block measures 14" between the heads at the manifold base, while a small block measure 12" between the heads at the manifold base.
  2. Facing the front of the engine, at the top surface of the timing chain area, to the left of the oil fill tube, there is a code about 1.5" high followed by the casting number. A letter indicates a big block, a number indicates a small block.
  3. A tell-tell sign is that the big blocks have a little hump in that area, whereas the small blocks are flat the whole way across.