I have a 1949 3100 bought new by my grandfather. I know for a fact this truck has never had a motor swap. the casting number is 3837004. The serial number (behind distributer by oil dipstick tube) prefix is BGCA
http://chevy.oldcarmanualproject.com/models/engine.htm#49engwith a build code of J108 (Oct 10th 48). This truck was ordered by my grand father with blue exterior/red interior with a heavy duty clutch and 4 speed floor shift/ dual action shocks front and rear/ dealer installed oil filter, and 2 taillamps. He passed this on to my father who has passed it on to me. I work for GM and asked our corporate rep about the casting code 3837004 wich was also used between 1955-57 on the 235-261 with the serial number including T56X. production started in later 55 for the 56 model year with over production units being put into earlier 57's. My 49 is titled by the serial number on the motor. I would be more than happy to post pics of the number on my title matching the serial number on the block with the casting code and production code. I wonder how many motors have been changed due to lack of research. It seems to me that the serial number behind the distributor is more important and will tell you more than the casting number 3837004
