Yes, always post your make, year, model truck (and engine size, if an engine question).

1948 GMC?
That might be the chassis serial number (Chevrolet did not stamp a serial number on the frame until around 1956, I think?)
FC102 19439

http://www.oldgmctrucks.com/page0010.html

F = 1947-1950
C = conventional cab (pickup)

102
10 = 1/2 ton
2 = long bed

Does that look familiar?