It's on the frame somewhere between the front cross member and the cowl. Could be very hard to find. Also, on frame under the body and on the transmission if the transmission is original.
On my '47, it's on the driver side frame under the hood, near the front of the engine compartment between the engine crossmember and the radiator, stamped on top of the frame rail.
My Long Beach made '47 sedan coupe has the number just forward of the front crossmember on the driver side. The engine was stamped on the top of the block toward the driver side rear corner. The trans also bears the same number. There could be more stampings, but I have not found them. Good Luck: Fred A