Per my parts books casting number 3733949 was used for ALL 1954 235 (exc PG) and 1955 1st series 235 trucks.
I'm betting by 1957 Chevrolet was scrounging around to find enough casting molds to make replacement blocks for the now obsolete engine (that had been out of production for 2+ years), so that they used whatever they had. So, you got a 235 casting number with sideways captian's bars (made with a screwdriver pushed into the sand cast) that was built as a 261 for warranty replacement. And since most vehicles were titled using the engine serial number prior to 1955/56 it was sent out with the serial number stamped on it from the factory confirming it's size and the exact customer it was going to.
Mike B
