FMC was trying to release new cars and trucks in 1948 but they haggled about the the design of the new Ford car. Bob Gregorie designed a new Ford car during the war but when it got close to production time after the war, Hank the Deuce was advised against using the design. The Mercury design was used but it was a more complicated car so it took longer to tool up. By the time the new shoe box Ford was ready for tooling, it was way too late to make the 1948 model year. The only designs that were ready were the Bonus Built trucks so they started production of the first of the 8BA designs in 1947 for the trucks. The Ford and Mercury cars were delayed another model year so they were 1949 models.
The initial new Ford and Mercury car designs were approved by Edsel Ford before he died in 1943. The original Ford car design didn't make it to US production but did make it to production in France as the Vedette. The coupe version looks like a miny Mercury but the fordor was still a sloper so it looked too dated for US production in the eyes of Hank the Deuce and his advisors. The 1949 Mercury design was used and it was the last Bob Gregorie design produced by Ford. Needles to say, Bob Gregorie exited Ford due to all the infighting over the final new Ford car design. There was a sloper design for the Lincoln and Mercury cars but it was never used in the Mercury final production cars. Only the Lincoln used the sloping rear roof design and that was only in 1949.
There are only a few casting numbers on an 8BA family of blocks that mean anything. As was mentioned date codes were stamped in to the top of the intake deck. Not all were stamped but most were. The Canadian blocks actually have the C8BA casting on the block but the only block casting on US production was a 1BA casting down inside the valve chamber to designate blocks that would be used with the new valves and the crankshaft to fit the automatic transmission. 8BA, 8CM, EAB, and EAC were prefix casting characters on the heads but heads can be swapped around same as intake manifolds.