There isn't one. Number is on transmission and on left frame rail in engine compartment. The patent plate on firewall SOMETIMES has abbrevited code for assembly plant, like ED for edgewater. I have heard that some late 48's had serial copied into a space on that plate, but I have looked at a lot and have never seen an example.
Your number should look like: *899A-(lengthy number)* That first bit just denotes 1948 239 passenger car. Different stuff there if 6 cylinder.
The location of the number can vary a bit because it was stamped by hand. The number was actually assigned to the engine/trans unit and stamped on the bell of the trans case just above the clutch inspection window. When that engine/trans unit was bolted into a chassis, they literally had a guy there with a set of number stamps and a big hammer who copied the number off the trans case onto the left frame rail. The only one you can see with the body on the frame is in the engine compartment. It can be anywhere between the front crossmember and firewall but usually next to the steering box. The other locations are about even with where the front seat is and on the arch over the rear axle. Of course the body would have to be off the frame to see those numbers.
The vin number on my 48 convert is on the left frame rail near the radiator. Should be the same on a coupe.
Its actually stamped into three areas on the left frame rail. Up front near the rad like everybody stated, at the center of the frame rail and at rear on or near 'the hump' over the axle. -Bigchief.
And the number 2 and 3 stamps generally are serial # only, without the prefix...I think this remained common practice on the "secret" locations even on much later cars...60's--70's GM were thus, anyhow.
I was lucky enough that the frame on my '48 had numbers visible at all three locations. Cool stuff.....
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