look for stamped numbers, somewhere near the top of the block, on the front or rear, near a corner. 8-xxxxxx configuration. The basic engine was used for 20 years or so. Bore changed from 3-1/4 to 3-3/8 in 1950.
These are 1948 Pontiac serial numbers, the engine number should match the vehicle serial number. 1941 was the last year American-built Pontiacs had the engine number different from the serial number. Starting in 1942, the engine number was the same as the serial number. Canadian serial numbers are different again. P6PB1001 to P6PB18146 C6PB1001 to C6P4765 L6PB1001 to L6PB4350 K6PB1001 to K6PB5552 W6PB1001 to W6PB3772 A6PB1001 to A6PB2926; and F6PB1001 to F6PB2951
interesting, my 1953 Motors only shows engine numbers through 41, and I didn't read it well enough to realize the two numbers were the same on later cars.
The Jalopy Journal
