That number looks like the engine serial number. It should have been stamped on a pad just to the rear of the distributor. The GCA prefix is for a '49 216 (built at Flint) that was used in the 4000 series trucks. The rest of the serial number is just the build sequence number.

A '49 216 used in a 3600 or 3800 would have the prefix AGCA or AGCM.


Curt
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1953 Chevy 6400, 1957 Chevy 2dr Sedan
--"Mediocrity is easy, the good things take time"