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