rickmg, If the block casting number is 3837004 (most likely) it's for a 1955 2nd Series - 57 235 with the large water pump hole. CON4 H 197 decodes as manufactured on:
CON4 = Conveyor 4
H = August
19 = 19th day of August
7 = 1957
Nothing on the machined pad to the left of the distributor base could indicate it is a replacement engine block/assembly. I would double check that surface, thoroughly scrubbing any dirt/debris and take/post a pic to show us what you see just to confirm the lack of a serial number.
The other 3 digit sets sound like sand casting numbers, usually found on the block and head - see pic below for sample pic showing the stacked 3 digit numbers on a 235 head. These do not specifically identify the engine. They were used by the original plant to select the sand castings used to cast the basic heads and blocks.
