Hi there and welcome to Chevy Chatter II. Glad to have you with us!
The information that you read on line was totally incorrect. The "2" means that your car was made in the Tarrytown, New York factory. And, the "AC" is the series designation for 1929. Neither has anything to do with the body style of the vehicle.
The "78231" is the number of the run, which means that your car was the 77,231st car made in the Tarrytown factory in 1929.
"2AC 78231" is the complete car serial number and the serial numbers started at 1,001 in 1929.