I friend of mine bought this 216 to put in his 36. He's asking what year it is and I can't answer that. I believe it's later than 39 but don't know that as fact. It has very small letter and number stamped on the boss by the distributor that I've not seen before which make me believe it was a replacement engine rather that factory installed.

With the cast circle it is a 1948=1951 block.

. Thanks for including a good pix of the engine casting number. If you look at web page <http://home.znet.com/c1937/Cast.htm> it's a 1950 - 51 engine. To the left (rear) of the dip stick is the date code C 3 0 which means March 3rd, 1950. It has a flat head and dome head screw which means it was made by the swing shift. The 1936 3 main bearing, 206 engine is slightly over an inch longer than the 1937 - 54 4 main bearing 216, 235 & 261 engines. You will have to alter the motor mounts slightly. The 1936 three speed transmission will bolt to the 1937 - 47 truck bell housing. .
. If you purchased a new engine from GM (Called crate engines today) they are shipped without any serial numbers and the installer is supposed to stamp the original serial number on the new block. I have a 54 261 engine that was installed in a 40 school bus. This is the correct replacement engine for a ton & half truck. So it has a 1940 truck serial on a 1954 truck engine. Using the 37 Chevy pictured in my avatar, It has a 1952 235 truck engine but the lazy mechanic, who installed it, didn't bother to stamp a number on it. .
. Good luck with your friend's project. .

A little clearifcation on serial numbers.
If you bought a bare block or a block with the crank shaft and pistons it had no stamped engine numbers anr block was not painted.

If a complete engine with oil pan, head, valve cover etc. it would have been taken off the engine plant line and have the nmbers stamped - just the same as an engne installed on the car assembly line and the engine and exposed parts painted as they would have been if installed in a vehicle,
A number of complete engines were kept in parts inventory.

Thank you gentlemen. I will pass that along.