Pre 1968 engines also had an engine unit number stamped on to the machined pad at the front of the RH head. Since this part is easily removed or replaced, use it for an indication, not a standard. Also starting in 1968, the VIN derivative of the engine's original car was stamped onto the vertical machined pad on the left side of the block, at the front, just under the head- block interface. It will generally match the Julian Day code cast into the heads, crankshaft, water pump, thermostat outlet, etc. A letter indicates a big block, a number indicates a small block.
Big blocks have a little hump in that area, whereas the small blocks have a completely flat shelf.
Small blocks from 1977 onward will have the CID or liters cast in large numbers right above the center core plug. The engine VIN number will also be cast onto the side of the block. But externally the distributor, valve covers, water pump, front cover, oil pan, carb, etc are the same. At least for '76. There was a problem in 1987.