How do you identify a flat head inline 6 engine?

The easiest way to identify a flat head engine is that there aren't any valve covers. The Cylinder head is what you see and you will notice alot of bolts. These are all the head bolts exposed, on a inline 6 cylinder there will usually be 33 bolts.

The cam is in the center of the engine and valves are not in the head like most engines. The head is, well, flat, and has the spark plugs on top of it, and inline 6 will have 6 spark plugs in a row.