According to my 1949 _MoToR's Auto Repair Manual_, the "serial number" found "on right front door pillar" and the "engine number" found "on top of cylinder block" are of the same series--171 for the 1947 Super Six--and we might infer that they should be identical. Your 17156300 would be, theoretically, number 56,200 in the series that began with 171101.
In my 1952 _Chilton Flat Rate Manual_, the 1940-47 cylinder head is part number 166268, the cylinder head water outlet is 166271, the thermostat with bypass is 166272, and so on. i don't see the bare block listed, but that set appears to confirm that the number (166270) you're seeing, wherever exactly you're seeing it, is a casting/part number.
According to the Chilton Flat Rate, your engine number should be found at "the top of the block, right side, between one and two exhaust manifold
flange." It should be the same number as the one you find on the "right front door hinge post." Again, 171 is the proper prefix for the 1947 Super Six.
God's Peace to you.
d
