what year is my flathead 40 or 41

39-41 blocks are identical, you can make sure you have this block by the "pencil ledge" cast into the block just above the timing gear cover. You can actually put a pencil there and it will not roll off. 59 blocks do not have this ledge, just a flat surface and will also have a large 59 cast into the bell housing part of the block. As far as raised intake surfaces, I have three of these engines and two came out of trucks (took them out myself) both had a cam marked 5T and were not releived around the valves
 
Typically a '40 will have two freeze plugs on each side on pan rails, out of sight with pan on but you can see two bulges above the plugs on each side of block. '41-up have the "raised" manifold surface, not actually raised but with shoulder, looks like an intake gasket is stuch there but is iron and edges outside that are not machined. These '41-2-wartime blocks do not have plugs in pan rail or the bulges that allow space for them.
 
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